___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
From the Sertolian syncytium to Sertoli cells in anamniotes, especially
Gymnophionan (Caecilian) Amphibians
J.-M. Exbrayat
Université de Lyon, UMRS 449, Laboratoire de Biologie Générale, Université Catholique de Lyon; Laboratoire de
Reproduction et Développement Comparé, EPHE/PSL; 10, place des Archives, 69288 Lyon Cedex 02, France
In Vertebrates, seminiferous tubes are bordered with an epithelium producing gametes included between Sertoli cells.
These cells were first described like a syncytium. With electron microscopy, the observations showed Sertoli cells
contained a single nucleus and were limited by a classical plasma membrane. Some studies showed the Sertoli cells of
anamniotes originated from follicle cells surrounding the cysts of germ cells. At the end of 1960’s the paradigm of
Sertolian syncytium was out. But Sertolian syncytium remained described during a long time. In anamniotes, Sertoli cells
constitute the wall of cysts grouping germ cells. In burrowing or aquatic lengthened gymnophionan (caecilian)
amphibians, the testes are constituted with several lobes containing locules in which spermatogenesis occurs. Light
microscopy indicated gametes were grouped in cysts included into a filamentous matrix containing fat globules. Some
nuclei were observed in a peripheral position. For a long time it was considered the Sertoli cells of these animals were
limited to those nuclei with a very small cytoplasm. The use of SEM and TEM revealed the matrix belonged to the
cytoplasm of Sertoli cells. The fibrous aspect corresponded to an artefact due to the fixative. The study of the testis
development showed Sertoli cells were giant cells delimited with a plasma membrane. Finally, in these amphibians, the
structure of Sertoli cells is reminiscent of the Sertoli cells belonging to other anamniotes.
Keywords: Sertoli cell, testis, germ cell, anamniote, amphibian, gymnophionan
1. Introduction
In Vertebrates, testes are constituted with seminiferous tubes or ampullae bordered with a germinal epithelium
producing gametes. This epithelium is put on a connective wall by a basal lamina. Endocrine Leydig cells are included
into connective tissue. Germinal epithelium is constituted with cells of spermatic lineage: spermatogonia, spermatocytes
I and II, spermatids and spermatozoa. This epithelium also contains somatic Sertoli cells between which are included
germ cells. This pattern is found in amniotes and anamniotes, with some differences in their organization. Firstly
studied in man and mammals, Sertoli cells were considered as merged, giving a syncytium. The use of TEM allowed
one to find Sertoli cells were well individualized, but a long time has been necessary to accept this new view of Sertoli
cells.
2. A brief story of the discovery of Sertoli cell
2.1 The discovery of Sertoli cells: syncytium or single cells?
Genital tracts were subject of interrogation since a long time. After several centuries of macroscopical observations and
deductions often imprinted with philosophy, the invention of microscope by Hooke and Van Leeuwenhoek allowed to
increase the knowledge of these organs. Van Leeuwenhoek (1632-1723) was one of the first to describe spermatozoa
(animalcule spermatici) in 1677. Later, Spallanzani in 1780, performing a famous experiment in frog, showed the
seminal fluid was at the onset of fertilization of female oocytes. XIXth was to be expected to meet several researchers
working on male gonads. Among these researchers, Sertoli published a first description of “branched cells” in human
testes [1]. These branched cells constituted the Sertolian syncytium. He also published fundamental observations on
spermatogenesis, resuming Von Ebner’s hypothesis [2]: the spermatozoa were issued from the branched cells. Sertoli
thought these cells performed a nutritional or mechanical role in spermatogenesis. He also showed spermatozoa were
coming from rounded spermatids (called nematoblasts), he described spermiogenesis dividing the development of
spermatocytes into three steps: leptotene/zygotene, pachytene, and diplotene. Spermatogonia were divided into two
stages. Sertoli observed some waves of spermatogenesis in which germ cells evolved grouped into isogenic series, and
linked each other with cytoplasm bridges.
2.2 The persistence of the “syncytium paradigm”
Sertoli cells were described in 1865 such as branched, i.e. like a syncytium, a cell mass with a lot of nuclei. But Sertoli
using only light microscopy, it was not possible for him to visualize the plasma membrane of these cells with this
technique. So, all nuclei appeared to be included into the same cytoplasm. Even Sertoli already suggested the branched
cells were a mass of single cells from which the limits could not be observed [3], the syncytium concept was integrated
into the scientific community, exceeding Sertoli himself. Regaud [4,5] was opposed to Sertoli’s deduction of cells with
167
___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
a single nucleus [6], and a lot of scientists adopted the “Sertoli syncytium” (Fig. 1). In the necrology of Pol Bouin
(1870-1962), Robert Courrier [7] spoke about the “Sertoli syncytium” studied by Pol Bouin and Paul Ancel which gave
about twenty publications in 1903 and 1904. In reports about the castration of foals performed by Bouin and Ancel, the
authors always spoke of a syncytium which was unique in seminiferous tubule; in cryptorchid pigs, they noted the
absence of Sertoli syncytium. Gopalakrishna studying the embryology of chiropterans noted: “the Sertoli cells are not
so distinctly marked out. Their nuclei are small and more densely stained, and they appear to be floating in the Sertoli
syncytium.” [8]
Fig. 1: Schematic representation of “Sertoli syncyticium”. The lumen of
seminiferous tubule is located on the upper part of picture. Basal lamina on which the
syncytium is put is located on the lower part. Germ cells are included into the
syncytium. 1: nuclei of Sertolian syncytium; 2: germ cells (oocytes II); 3:
spermatozoa ready to be released in the lumen; 4: Sertoli syncytium.
.
During several years, “Sertoli syncytium” was always used but some authors were lesser precise than others. Allen
explained the “indifferent cells (another name given to Sertoli cells) had very slight if any visible membranes” [9]. AasJorgensen spoke about the scarcity of cells with several nuclei in the testis [10]. Yet, some authors at the beginning of
XXth considered Sertoli cells being well-delimited units, like most other cells [11, 12], others considered the cell
membranes were destroyed by fixative [13].
Observed with light microscope, the limits of Sertoli cells were not visible or very little visible, the cytoplasm was
clear, nucleus oval with a big nucleolus and a characteristic indentation which permitted to recognize them among the
germ cells. They seemed to be never mitotic in adult. When TEM generalized in biology, the observations showed
Sertoli cells were limited with a classical plasma membrane and contained a single nucleus [14,15], even if sometimes it
was not possible to visualize these limits with electron microscope [16]. Fawcett and Burgos rejected the concept of
germ cells included into Sertoli cells for they observed plasma membranes separating the two kinds of cells [17] (Fig.
2). Sapsford et al. did not visualize the limits of Sertoli cells but they dissociated Sertoli cells from seminiferous
tubules, showing they were cells with a single nucleus [6, 18, 19]. From the time at which the true structure of Sertoli
cell has been established, a lot of studies using electron microscopy were published, permitting to understand the
relationships between Sertoli and germ cells. Some studies also showed the Sertoli cells of anamniotes originated from
follicle cells surrounding the cysts of germ cells [20]. Finally, at the end of 1960’s one could think the paradigm of
Sertoli syncytium was out. But it was not exact.
Fig. 2: Schematic representation of Sertoli cells in amniotes. The lumen of
seminiferous tubule is located on the upper part of picture. Basal lamina on which the
Sertoli cells are put is located on the lower part. Germ cells are included between
Sertoli cells. 1 and 1‘: nuclei of two cells; 2: germ cells (oocytes II); 3: spermatozoa
ready to be released in the lumen; 4: Sertoli cell.
.
168
___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
2.3 From syncytium to single cell
In several books for teaching, Sertoli syncytium was described during a long time. In 1967, Houillon spoke about
“Sertoli syncytium” [21], but he also specified the limits of cells were hard to see. In 1973, Gallien also spoke about a
Sertoli syncytium highlighted into ductules without any sperm cell in the cases of free-martin [22]. Boue and Chanton
explained Sertoli cells anastomosing to form a syncytium [23]. It is easy to imagine a more or less long time (2 to 3
years) can pass without any update between the redaction of a book and its publication. But, curiously the Sertoli
syncytium was found in several more recent articles: some authors [24,25] explained the germ cells of the snake
Tantilla hobartsmith were packed into a Sertoli syncytium. A comparable situation was described in the snake
Seminatrix pygmaea [26].
3. Sertoli cells in anamniotes
3.1 Sertoli cells in Agnathans, Chondrychtyans, and Osteichtyans
The first studies about Sertoli cells concerned man, then mammals and other amniotes (reptiles and birds), and
currently, a lot of studies concerning mammals were published [20]. Few works were devoted to anamniotes’ Sertoli
cells. In anamniotes of which sexual cycles are frequently discontinuous, successive generations of germ cells may be
found at each spermatogenic wave [27].
In Agnathans, somatic cells were described in testes [28]. They were called “vegetative cells” [29], “link cells” or
“Sertoli cells [30]. In Osteichtyans, the organization of seminiferous tubules was described in several species [31]. They
were described In Latimeria chalumnae [32], Protopterus sp. [33]. In Teleosteans, seminiferous tubules or locules are
limited with a layer of somatic cells sometimes called “Sertoli cells”, “follicle cells”, or “connective cells”. For other
authors, cells looking like amniote’s Sertoli cells were called “lobules boundary cells” [34,35]. Histochemical
investigation showed these cells possessed a steroidogenis glandular function, and some authors considered them to be
the equivalent to Leydig cells [34, 36-44]. Henderson also spoke about “link cells” but without attributing them any
endocrinal function [45]. Some authors considered Sertoli cells or link cells such as a syncytium [37,38].
In the abundant literature of the three first thirds of XXth, the terminology of Sertoli cells or link cells in
Osteichtyans was well variable, and a steroidogen function could or not be attributed to these cells. Studies from 1960
showed these Sertoli cells able to synthesize steroid hormones. So some authors proposed to speak about Sertoli cells in
all the cases [31]. Using TEM, these authors studied them in species performing a yearly reproductive cycle in order to
observe testes filled with all the stages of germ cell or, contrarily, containing only spermatogonia. These observations
gave well contrasted situations of the same structure throughout time. The species studied were Salmo trutta and S.
gairdneri in which follicle cells or link cells were described, Esox lucius with link cells, Cyprinus carpio with Sertoli
cells, and Rutilus rutilus with lobules boundary cells or Sertoli cells. During quiescence, Sertoli cells surrounded
isolated or pair-grouped spermatogonia [31]. At spermatogenesis, each spermatogonium divided, daughter cells being
separated each other with Sertoli cells. Each spermatogonium originated a cyst in which divisions were synchronous
(isogenic series). Into each cyst, spermatogenesis was independent from the other cysts. At the end, when spermatozoa
were formed, the cyst wall constituted with the well thin cytoplasm of Sertoli cell, opened and spermatozoa evacuated
into the tubule. Sertoli cells became now against the wall of seminiferous tubule. Some of them lost fragments of
cytoplasm at the spermatozoa evacuation.
The first studies about Sertoli cells In Chondrichtyans were published by Swaen and Masquelin [46], and Stephan
[47]. TEM permitted to precise the structure and ultrastructure of Sertoli cells in Selachians throughout spermatogenesis
[48,49]. Like in Osteichtyans, the Chondrichtyan seminiferous tubules were constituted with several cysts still called
ampullae in which spermatogenesis occured synchronously in each one. These cysts originated from the spermatogonia
situated in a ventral position into the testis of Scyliorhinus canicula [48]. Throughout their evolution, these cysts
constituted with isogenic series of germ cells, migrated in a dorsal position and finished to empty mature spermatozoa
in efferent ductules. The empty cysts degenerated. The differentiation of a seminiferous tubule began with the
association of a Sertoli cell and a spermatogonium. In Selachians, Sertoli cells contained “problematic bodies” [50]
corresponding to proteins involved in the epithelium lysis when spermatozoa became free. Several successive divisions
of both the two cell types drove to the increase of seminiferous tubule. Each Sertoli cell was then associated to several
germ cells divided in a synchronous manner, giving isogenic series. Several cysts were observed with different states of
spermatic differentiation into the same seminiferous tubule. At meiosis, Sertoli cells increased. In Squalus acanthias,
when spermatozoa became mature, they were thrown into the lumen after degeneration of all or part of Sertoli cell in
which spermatozoa were included, with the presence of “problematic bodies” [48].
3.2 Sertoli cells of anuran and urodelan amphibians
In amphibians, some authors published literature showing an organization looking like that of other anamniotes [51,52]
(Fig. 3). During spermatic activity, the spermatozoa issued from the proliferation of germ cells grouped into
homogenous cysts limited with follicle cells (these follicle cells were in fact the first stage of Sertoli cells). In Anura,
169
___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
the cells surrounding the cyst increased, becoming steroidogenous. They separated from the germ cells having reached
the spermatozoa stage, by the aperture of the cyst. Follicle cells now free from germ cells became Sertoli cells and
looked like amniotes’ ones. A study with TEM performed in the toad Bufo arenarum showed these Sertoli cells were
well limited by a plasma membrane and were not grouped such as a syncytium [53]. These authors also noted the shape
modification of these cells from the time at which they were follicle cells surrounding the isogenic series of germ cells,
and the time at which the cysts contained spermatids or spermatozoa. At this time, the structure of amphibian Sertoli
cells looked like anamniote’s ones even if Lofts insisted on the difference between anamniote and amniote Sertoli cells
[51,52].
Fig. 3: Schematic representation of Sertoli cells
in anamniotes. The lumen of seminiferous
tubule is located on the upper part of picture.
Basal lamina on which the syncytium is put is
located on the lower part. Germ cells are
included between Sertoli cells, grouped in order
to form cysts which are clusters grouping cells
at the same stage of differentiation. 1:
oogonium; 2: germ cell (oocytes II); 3: nucleus
of Sertoli cell; 4: Sertoli cell; 5: germe cell
(oocyte I ready tobe released in the lumen; 6:
spermatozoa ready o be released in the lumen.
7: Sertoli cell (follicle cell) opened to release
spermatozoa.
3.3 Sertoli cells in gymnophiona (Caecilians)
Gymnophionan amphibians have a special place among the anamniotes [54]. These lengthened and burrowing animals
live on tropical areas. They possess several specific characteristics. The testes are constituted with several lobes which
can be more or less fused. Each lobe contains several locules, in which spermatogenesis occurs. Each locule is linked by
a duct to the rete testis in which spermatozoa are driven to the cloaca using the Wolffian ducts. The locules are
separated each other with connective tissue containing steroidogenic Leydig cells. The disposal of gem cells is specific
to Gymnophiona. The primary spermatogonia are situated at the onset of evacuative duct, secondary spermatogonia are
situated against the wall of locule, and spermatocytes I and II, spermatids and spermatozoa differentiate in displacing
toward the centre of locule. With light microscopy, cells belonging to the same stage are grouped in cysts seeming
included into a filamentous matrix containing fat globules. Nuclei looking like the nuclei of Sertoli cells in the other
vertebrates were observed in a peripheral position (Fig.4). This description is that which has been given since along
time [55-58]. Seshachar considered these Sertoli cells were limited to nuclei contrarily to that it was known in other
vertebrates (in which it was still a syncytium) [59]. Then no work about these cells in Gymnophiona was published
during a long time.
Fig. 4: Transversal section of a lobe of Typhlonectes
compressicauda testis. Staining: Masson-Goldner trichroma.
Each lobe is divided into several locules. Each locule is filled
with a gelatinous and filamentous matrix which corresponds to
the cytoplasm of Sertoli cells. Germ cells seem to be included
into this matrix, but they are grouped into clusters which are
really included between Sertoli cells. ed: evacuating duct; gc:
germ cells (here, spermatocytes) included into a cyst; loc:
locule; m: matrix (cytoplasm of Sertoli cells); IT: interstitial
tissue (Leydig cells); z: spermatozoa ready to be expulsed. Scale
bar = 30µm.
In 1986, Exbrayat resumed the study of Caecilian testis using particularly SEM and TEM [60]. These methods
helped to understand the matrix was in fact the cytoplasm of Sertoli cells (Fig. 5). The fibrous aspect observed with
170
___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
light microscopy corresponded to an artefact linked to the fixative. With SEM, these filamentous structures among them
nuclei were scattered corresponded to the collapsus of cytoplasm structures. With TEM, it was obvious that Sertoli cells
were particularly large. In the cytoplasm vesicles seemed empty but they were certainly filled with lipids before the
operation of fixation and preservation into ethanol. The study of the testis development in embryos and young animals
showed the evolvement of Sertoli cells showing it was well giant cells, delimited with plasma membranes [60-63] (Fig.
6). Finally, a lot of fat vesicles are included into the cytoplasm of these Sertoli cells, giving a general aspect optically
empty; nuclei included in this cytoplasm look like separated units which can be well observed with both TEM and SEM
(Fig. 7). This new vision of the structure of gymnophionan Sertoli cells has been published for the first time in 1994
[64]. Since this time, the structure of locules and Sertoli cells in Gymnophiona were completed [65-68]. Finally, in
these amphibians, the structure of Sertoli cells is reminiscent of the Sertoli cells belonging to other anamniotes [52,69]
Fig. 5 Typhlonectes compressicauda testis. Left picture: SEM observation of a lobe of Typhlonectes compressicauda testis. Germ
cells are included into cysts dispersed between Sertoli cells the nucleus of which being found against the peripheral wall of locule.
Scale bar = 30 µm. Right picture: TEM observation of a locule of Typhlonectes compressicauda testis. Germ cells (here,
spermatocytes) are included between the Sertoli cells. The cytoplasm of these ones is filled with substances looking like a matrix.
Scale bar = 3 µm. CS: peripheral nucleus of Sertoli cell; C1: 1st spermatocyte; G1: 1st spermatogonium observed against the
peripheral wall of locule; m: matrix (cytoplasm of Sertoli cell; S: cytoplasm of Sertoli cell (also called “matrix”).
Fig. 6 Typhlonectes compressicauda testis. Left picture: transversal section of testis belonging to Typhlonectes compressicauda
new-born. Locules are small, separated with interstitial tissue. Germ cells (oogonia) are situated near a small evacuating duct. Small
Sertoli cells develop with a small matrix (cytoplasm). Scale bar = 8 µm. Right picture: transversal section of testis belonging to
Typhlonectes compressicauda lesser than one year-old. Sertoli cells develop with a more abundant matrix (cytoplasm). Germ cells
remain against the wall of testis, and they become farer from the evacuating duct. Scale bar = 8 µm. ED: evacuating duct; GC: germ
cell (oogonium); IT: interstitial tissue; M: matrix.
171
___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
Fig. 7 Typhlonectes compressicauda Sertoli cells. Left picture: a nucleus of Sertoli cell observed with TEM, with characteristic
indentations. Scale bar = 1.5 µm. Right picture: a part of f Sertoli cell containing the nucleus observed with SEM. Scale bar = 1 µm
4. Conclusions
In the first descriptions, with the use of light microscopes exclusively, Sertoli cells were considered such as a syncytium
filling all the seminiferous tubules and in which germ cells were included. Evolution of light microscopy did not allow
going further in the appreciation of the structure of these cells for plasma membrane never has been highlighted. This
was perhaps a fixative effect but also due to the complexity of the imbrication between Sertoli and germ cells.
In the 1950s and 1960s the use of TEM allowed to precise the exact nature of these cells showing the plasma
membranes. The first works about these cells were performed in amniotes. Other studies also showed such cells in
anamniotes in which a constant was observed: Sertoli cells first surrounded a spermatogonium which will give an
isogenic series of germ cells, constituting a cyst which stays enveloped into the Sertoli cell. At the end of
spermatogenesis, these Sertoli cells modify to give cells looking that of amniotes. Curiously, the syncytium notion
persisted several years after the discovery of the plasma membrane and, still to-day, several papers give reference to
Sertoli syncytium.
After these morphological works. others studies allowed to understand the activity of Sertoli cells [20], sustaining as
well as nutritive cells, with a phagocytic activity, ridding the seminiferous tubules of degenerated germ cells, which is
manifested by the accumulation of lipids. Sertoli cells are the target of FSH and testosterone, they secrete the antiMüllerian hormone at the origin of the regression of Müllerian duct in males, excepted in some anamniotes such as
anuran amphibians the males of which keeping sometimes vestigial Müllerian duct, and mostly Gymnophionan in
which Müllerian ducts persist in males with a gland function participating to the sperm composition with an activity
comparable to that of the prostate in mammals [70,71].
Acknowledgements Author thanks Catholic University of Lyon (UCLy) and Ecole Pratique des Hautes Etudes (EPHE) that allowed
the freedom in organizing his research field and supported his work. He also thanks colleagues and students who participated since
more than 35 years, to the studies on Gymnophionans.
References
[1] Sertoli E. Dell’esistenza di particolari cellule ramificate nei canalicoli seminiferi del testicolo umano. Morgagni. 1865; 7:31–40.
[2] Von Ebner V. Untersuchungen iiber den Bau der Samencanalchen und die Entwicklung der Spermatozoiden bei den Saugethieren
und beim Menschen. l7ist. Phys. u. Hist. Graz, 1871 (Leipzig).
[3] Sertoli E. Sulla struttura dei canalicoli seminiferi dei testicoli studiata in rapporto allo sviluppo dei nemaspermi. Archivio per les
Scienze Medichi. 1878; 2:107-146.
[4] Regaud C. Sur la morphologie de la cellule de Sertoli et sur son rôle dans la spermatogénése chez les mammifères. Comptes
rendus de l’Association des Anatomistes. 1899; 1:21–31.
[5] Regaud C. Etudes sur la structure des tubes séminifères et sur la spermatogénèse chez les mammifères. Archives d’Anatomie
Microscopique.1901; 4:101–56.
[6] Sapsford CS. The development of the Sertoli cell of the rat and mouse: its existence as a mononucleate unit. Journal of Anatomy,
London. 1963; 97:225-38.
[7] Courrier R. Notice sur la vie et les travaux de Pol Bouin. Académie des Sciences, Notices et discours. 1962; 4:590-624.
[8] Gopalakrishna, A. Studies on the embryology of Microchiroptera. Proceedings of Indian Academy of Sciences B. 1947; 27: 13750.
[9] Allen E. Studies on degenerating sex cells in immature mammals. I. An analysis of degeneration in primordial and large germ
cells in male albino rats aged 1-9 days. Journal of Morphology. 1949; 85:405-21.
[10] Aas-Jorgensen E, Funch JP, Engel PF, Dam H. The role of fat in the diet of rats. 9. Influence on growth and histological findings
of diets with hydrogenated peanut oil or no fat, supplemented with linoleic acid or raw skim milk, and of crude casein compared
with vitamin Test Casein. British Journal of Nutrition. 1956; 10:292-304.
172
___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
[11] Hoven H. Histogenèse du testicule des mammifères. Anatomisher Anzeiger. 1914; 47:90-109.
[12] Stieve H. Die Entwicklung der Keimzellen und der Zwischenzellen in der Hodenanlage des Menschen. Ein Beitrag zur
Keimbahnfrage. Zeitschrift für Mikroskopisch Anatomische Forschun, 1927; 10:225-85.
[13] George U. Beobachtungen an Sertolizellen im Hoden des Menschen und der Ratte. Zeitschrift für Mikroskopisch Anatomische
Forschun. 1937; 42:479-98.
[14] Nicander L, Abdel-Raouf M, Crabo B. On the ultrastructure of the seminiferous tubules in bull calves. Acta Morphologica
neerlandensis. Scandinavia. 1961; 4:127-35.
[15] Engle ET.: The male reproductive system. In Lansing A. I., editor, Cowdry’s Problems of Ageing. Williams and Wilkins
Company, Baltimore, 1952. 708-729.
[16] Watson NL. Spermatogenesis in the albino rat as revealed by electron microscopy. Biochimica et biophysica Acta, 1952; 8:36974.
[17] Fawcett DW, Burgos MH. The fine structure of the Sertoli cells in the human testis. Anatomical Record. 1956; 124:401–2.
[18] Sapsford et al. Sapsford C.S.: The development of the testis of the Merino ram, with special reference to the origin of the adult
stem cells. Australian Journal of agricultural Research. 1962a, 13, 487-502.
[19] Sapsford CS. Changes in the cells of the sex cords and seminiferous tubules during the development of the testis of the rat and
mouse. Australian Journal of Zoology. 1962b; 10:178-92.
[20] França LR, Hess A, Dufour JM, Hofmann MC, Griswold MD. The Sertoli cell: one hundred fifty years of beauty and plasticity
Andrology. 2016; 4:189–212.
[21] Houillon C. Sexualité, Paris: Hermann; 1967.
[22] Gallien L. Différenciation et organogenèse sexuelle des métazoaires. Paris: Masson et Cie; 1973.
[23] Boue H, Chanton R. Zoologie, Tome 2.2. Paris: Doin; 1975.
[24] Goldberg SR, Parker WS. Seasonal testicular histology of the colubrid snakes, Masticophis taeniatus and Pituophis
melanoleucus. Herpetologica. 1975; 31:317–22.
[25] Goldberg SR. Reproductive cycle of smith’sblack-headed snake Tantilla hobartsmith (Serpentes: Colubridae) in Arizona 1975.
Western North American Naturalist. 2004; 64:141-3.
[26] Sever DM, Stervens RA, Ryan TJ, Hamlett WC. Ultrastructure of the Reproductive System of the Black Swamp Snake
(Seminatrix pygaea). III. Sexual Segment of the Male Kidney. Journal of Morphology. 2002; 252:238-54.
[27] Lofts B. The Sertoli cell. General and Comparative Endocrinology, supplt. 1972; 3:636-48.
[28] Cunningham JT. Spermatogenesis in Myxine glutinosa. Quartely Joutrnal of Microscopical Science. 1891; 33:169-85.
[29] Shreiner A, Shreiner KE. Uber die Entwicklung der männlichen Geschlechts-zellen von Myxine glutinosa (L.) I.
Vermehrungsperiode, Reifungsperiode und Reifungsteilungen. Archives de Biologie 1905; 21:304-14.
[30] Chieffi G, Botte V. Il tessuto intertiziale del testicolo dei ciclostomi.Ricerche istologiche ed istochimiche in Lampetra fluviatilis
e Lampetra planeri. Rendiconti dell’Istituto delle Scienze di Camerino. 1962; 3:90-94.
[31] Billard R, Jalabert B, Breton B. 1972. Les cellules de Sertoli des poissons téléostéens. I. Etude ultrastructurale. Annales de
Biologie Animale, Biochimie, Biophysique. 1972; 12:19-32.
[32] Tuzet O, Millot J. La spermatogenèse de Latimeria chalumnae Smith (Crossoptérygien coelacanthidé). Annales des Sciences
Naturelles, Zoologie, 12ème série. 1959; 61-69.
[33] Boisson C. Spermatogenèse de Protopterus annectens (Dipneuste) du Sénégal. Annales de la Faculté des Sciences de Dakar,
1961; 6:133-44.
[34] Marshall AJ, Lofts B. The Leydig-cell homologue in certain Teleost fishes. Nature; 1956; 177:704-5.
[35] Hardisty MW, Rothwell B, Steele K. The interstitial tissue of the testis of the Rive lamprey, Lampetra fluviatilis. Journal of
Zoology. 1967; 152:9-18.
[36] Lofts B, Marshall AJ. Cyclical changes in the distribution of the testis lipids of a teleost fish Esox lucius. Quartely Journal of
Microscopical Science. 1957; 98:79-88.
[37] Robertson OH. Accelerated development of testis afterv unilateral gonadectomy with observations on normal testis of Rainbow
trout. Fish. Bulletin of Fisheries Widlife Service. 1958; 58:9-30.
[38] Marshall AJ. Reproduction in male bony fish. Symposia of the Zoological Society of London. 1960; 1:137-151.
[39] Rai BP. Cyclical changes in the testis of the mahseer Barbus tor (Tor tor). Acta anatomica. 1965; 62:461-75.
[40] Yaron Z. 1966. Demonstration of 3 β-hydroxysteroid dehydrogenase in the testis of Tilapia mossambica. Journal of
Endocrinology. 1966; 34:127-8.
[41] Ashan SN. Cyclical changes in the testicular activity of the lake chub, Couesius plombeus (Agassiz). Canadian Joural of
Zoology. 1966; 44:149-59.
[42] Khanna SS, Pant MC. Structure and seasonal changes in the testes of a hill stream fish Glyptosternum pectinopterum. Japanese
Journal of Ichthyology. 1966; 14:110-9.
[43] Moser HG. Seasonal histlogical changesin the gonads of Sebastodes paucispinis Ayres, an ovoviviparous teleost (Family
Scorpaenidae). Journal of Morphology. 1967; 123:329-53.
[44] O’Halloran MJ, Idler DK. Identification and distribution of the Leydig cell homologous in the testis of sexually mature atlantic
salmon (Salmo salar). General and Comparative Endocrinology. 1970; 15:361-4.
[45] Henderson NE. The annual cycle in the testis of the eastern brook trout, Salvelinus fontinalis (Mitchill). Canadian Journal of
Zoology. 1962; 40:631-41.
[46] Swaen A, Masquelin H. Etudes sur la spermatogenèse. Archives de Biologie, Liège. 1883; 4:741-801.
[47] Stephan MP. Sur le Développement de la cellule de Sertoli chez les Sélaciens. Comptes Rendus de la Société de Biologie. 1902;
54:773-5.
[48] Collenot G, Damas D. Etude ultrastructurale de la cellule de Sertoli au cours de la spermiogenèse chez Scyliorhinus canicula.
Cahiers de Biologie Marine. 1980; .21:209-19.
[49] Pudney J, Callard GV. Development of agranular reticulum in Sertoli cells of the testis of the dogfish Squalus acanthias during
spermatogenesis. Anatomical Record. 1984; 209:311-21.
173
___________________________________________________________________________________________
Microscopy and imaging science: practical approaches to applied research and education (A. Méndez-Vilas, Ed.)
[50] Semper C. Das urogenitalsystem der plagiostomen und seineBedeutung für das der übrigen Wirbelthire. Arbeiten. ZoologishZootomishe, Institute in Würzburg 1875; 2:195-509.
[51] Lofts B. (1968), Patterns of testicular activity. In Perspectives in endocrinology, Barrington and Jorgensen (Ed.), Acad. Press;
239-304.
[52] Lofts B, Bern HA. 1972 The functional morphology of steroidogenic tissues. In Idler, D.R. editors. Steroids in non-mammalian
vertebrates, New York, Academic Press, 1972. p. 37-125
[53] Burgos MH, Vitale-Calpe R. The fine structure of the Sertoli cell-spermatozoan relationship in the toad. Journal of
Ultrastructural Research. 1967; 19:221-37.
[54] Exbrayat, JM, Raquet M.. Chapter 4: Vertebrate evolution: the strange case of Gymnophionan Amphibians. In: Pontarotti, P,
editor. Evolutionary biology: concept, modeling, and application. Berlin Heidelberg: Springer-Verlag; 2009. p. 71-89.
[55] Spengel JW. Das Urogenitalsystem der Amphibien. I. Theil. Der Anatomische Bau des Urogenitalsystems. Arbeit der
Zoologische-Zootomie Institute Würzburg. 1876; 3:51-114.
[56] Tonutti E. Beitrag zur Kenntnis der Gymnophionen. XV. Das Genitalsystem. Morphologische Jahrbuch. 1931; 68:151-292.
[57] Seshachar BR. The spermatogenesis of Ichthyophis glutinosus (Linn.).I. The spermatogonia and their division. Zeitschrift für
Zellforschung und Mikroskopische Anatomie. 1936; 24, 662-706.
[58] Wake M.H. Evolutionary morphology of the caecilian urogenital system. Part I: the gonads and fat bodies. Journal of
Morphology. 1968; 126:291-332.
[59] Seshachar BR. The Sertoli cells in Apoda. Journal of Mysore University. 1942; 3:65-71.
[60] Exbrayat JM. Quelques aspects de la biologie de la reproduction chez Typhlonectes compressicaudus (Duméril et Bibron, 1841),
Amphibien Apode. Doctorat ès Sciences Naturelles. Paris 6 University. 1986.
[61] Exbrayat JM. Le testicule de Typhlonectes compressicaudus : structure, ultrastructure, croissance et cycle de reproduction.
Mémoires de la Société Zoologique de France. 1986b; 43: 121-132.
[62] Anjubault E, Exbrayat JM. Contribution à la connaissance de l’appareil génital de Typhlonectes compressicauda (Duméril et
Bibron, 1841), Amphibien Gymnophione. I. Gonadogenèse. Bulletin mensuel de la Société linnéenne de Lyon. 2004 ; 73:37992.
[63]Anjubault E, Exbrayat JM. Contribution à la connaissance de l’appareil génital de Typhlonectes compressicauda (Duméril et
Bibron, 1841), Amphibien Gymnophione. II. Croissance des gonades et matutrité sexuelle des mâles. Bulletin mensuel de la
Société linnéenne de Lyon. 2004 ; 73:393-405.
[64] Exbrayat JM, Dansard C. Apports de techniques complémentaires à la connaissance de l’histologie du testicule d’un Amphibien
Gymnophione. Revue française d’Histotechnolodie. 1994; 7:19-26.
[65] Smita M, Oomen VO, George Jancy M, Akbarsha MA. Sertoli cells in the testis of Caecilians Ichthyophis tricolor and
Uraeotyphlus cf. narayani (Amphibia: Gymnophiona): light and electron microscopic study. Journal of Morphology. 2003;
258:317-26.
[66] Smita M, Oomen VO, George Jancy M, Akbarsha MA Stages in spermatogenesis of two species of caecilians Ichthyophis
tricolor and Uraeotyphlus cf. narayani (Amphibia: Gymnophiona): light and electron microscopic study. Journal of
Morphology. 2004a; 261:92-104.
[67] Smita M, George Jancy M, Girija, R, Akbarsha MA, Oomen VO. Spermiogenesis in caecilians Ichthyophis tricolor and
Uraeotyphlus cf. narayani (Amphibia: Gymnophiona). Analysis by light and transmission enectron microscopy. Journal of
Morphology. 2004b; 262:484-99.
[68] Smita M, George Jancy M, Akbarsha MA, Oomen VO; Exbrayat JM.2006. Spermatogenesis. In: Exbrayat JM, editor.
Reproductive Biology and Phylogeny of Gymnophiona. Enfield, Jersey, Plymouth: Science Publishers; 2006. p. 231-246.
[69] Tso E CF. An ultrastructural study on the Sertoli cell in the newt (Trituroides hongkongensis). Acta Zoologica. 1974; 35:217-23.
[70] Wake, MH. Structure and function of the male Mullerian gland in Caecilians (Amphibia: Gymnophiona), with comments on its
evolutionary significance. Journal of Herpetology. 1981; 15:17-22
[71] Exbrayat JM. Cycle des canaux de Müller chez le mâle adulte de Typhlonectes compressicaudus (Duméril et Bibron, 1841),
Amphibien Apode. Comptes rendus des Séances de l’Académie des Sciences, Paris. 1985; 301:507-12.
174