184
NOTES AND CORRESPONDENCE.
On the Structure of Amphora, a genus of Diatomacese, and the
Diagnosis of its Species.—When Linnaeus said that all objects
of natural history must have a specific name, he did not mean
a trivial name (which was not then invented) j but what is called
a short, distinctive character, otherwise it is not imperative on
others to adopt the trivial name imposed, or recognise it in any
way. The want of short characters (intended to place clearly
before the mind the few essential points of difference between
supposed new and already known forms or species) cannot be
supplied by figures or diffuse descriptions of the entire object,
as these leave quite in the dark the precise marks of distinction observed By the writer, if such actually existed. In
composing either a defining character or a detailed description, it is also necessary to use the technical language of that
science. Recently, in referring to Dr. Gregory's paper on
the Diatomacese of the Clyde, published in the last part of
the ' Transactions of the Royal Society of Edinburgh/ I
regretted that this patient observer had; neglected these
rules, and thus enveloped his whole memoir in an almost
impenetrable cloud; thus not only precluding himself from
claiming any right of priority of names, in the event of
the same form being afterwards correctly characterised by
another under a different name, hut depriving the paper
itself of its claims to be considered a scientific one. The
same unfortunate cloud renders it difficult to understand
what Dr. Gregory's actual views of the structure of Amphora are; although, from expressions used by him, he
appears to enunciate the theory, that what other writers call
a simple frustule, ought to be considered as a double one.
To make this more intelligible to those not generally
interested in such pursuits, I would refer to the structure
of a diatom, as explained by Smith in his ' Synopsis of
British Diatomacese;' and recommend the mode of proving,
by Canada balsam, whether the frustule is single or double.
When tested in this way, what is commonly called a simple
frustule is found to be actually so, and of one cell, so
that Dr. Gregory's hypothesis is untenable. The structure of the genus Amphora appears to have been also
slightly misunderstood by Kutzing and Smith. The real
form of the frustule is not a spheroid, as they must have
considered it, but rather like that of a coffee-bean, rounded
at the back and hollowed out in front, the line connecting
MEMORANDA.
185
the two terminal and central nodules of each valve being the
median line; this line and the central nodule are thus not
marginal, as hitherto described, but exactly as in other
diatoms in which such are found. An Amphora would thus
chiefly differ, by the half of the valve on the one side of the
median line being concave, while the other was convex;
whereas, in most genera of the group the two halves of the
valve are precisely alike.
The form and structure of the frustule being established,
the parts capable of affording good distinctive marks for species
next require to be examined. All naturalists agree, that if these
are taken from variable parts, they must be of less importance
than if derived from those that are subject to little or no
variation; and that no observation can be relied on, of a
permanent kind, when taken from parts known to change
their appearance rapidly. Thus, the zone connecting the two
valves of a diatom, which, from being a mere line, is understood to attain the whole breadth of the frustule in the course
of twenty-four hours, has been deservedly rejected; and
hence it is to be feared that few or none of Dr. Gregory's
species of "Complex Amphorae," which owe their peculiar
appearance to it, will stand the test of diagnostic characters.
As the strise, costse, or furrows, are the same on both sides of
the median line, and as the valve is folded, those at the back
of the frustule must be seen through the medium of the surface nearer the eye, and crossing those belonging to it, so that
observations on these relate entirely to the accidental position
the frustule happens to be in. This compels one to depend
chiefly for essential characters—1st, on the small portion that
is seen between the median line and the apparent outline of
the frustule; and 2d, on the form of the frustule itself, previous to the siliceous connecting zone commencing the process
of self-division.
No certain conclusions can be drawn as to what is a new
form or species from deposits or dredgings, on account of the
impossibility of procuring the species in an isolated state, and
consequently of studying them independently; the same
species putting on very different aspects, and different species
assuming the same aspect at particular stages of self-division.
Some species of diatoms have both an habitual and an
accidental appearance. Thus the whole genus Pleurosigma is
habitually sigmoid; but P. cestuarii, P. strigosum, and some
others occasionally appear reversed or twisted, both extremities being on the same side of the median line; P. reversum,
fig. 105 of Dr. Gregory's paper, will illustrate an accidental
state; the whole supposed new genus Toxonidea of Donkin
186
MEMORANDA.
is formed of species of Pleurosigma in the same predicament.
On the other hand, the entire genus Cymbella is habitually
reversed, although specimens may occur assuming accidentally
the appearance of a Pleurosigma. These accidental appearances are sometimes caused by actual resupiuation, sometimes from preparing to form spores, and sometimes by a
mere change of position.
Microscopical differences are by themselves of little importance. To see is one thing; to understand and combine
what we see, another: the eye must be subservient to the mind.
Every supposed new species requires to be separated from its
. allies, and then subjected to a series of careful observations
and critical comparisons. To indicate many apparently new
species is the work of an hour, to establish only one on a sure
foundation is sometimes the labour of months or years. In
microscopical natural history as much scrutiny is required to
prove a new form to be distinct from its allies as in chemistry
to discover a new alkaloid, or in astronomy to demonstrate
the identity of two comets. A naturalist cannot be too
cautious. It is better to allow diatoms to remain in the
depths of the sea, or in their native pools, than, from imperfect materials, to elevate them to the rank of distinct species,
and encumber our catalogue with a load of new names so ill
defined, if defined at all, that others are unable to recognise
them; the same object can be more easily attained by attaching them, in the mean time, to some already recorded species,
with the specific character of •which they sufficiently accord.
In all such cases the question to be solved for the advantage
of naturalists is not, whether the object noticed be a new
species, but whether it has been proved such, and clearly
characterised.—E. WALKER-ARNOTT, Dowanhill, near Glasgow.
On the Structure of Ehafedonema and other Diatomacese
•with compoTittd frustules.—It is witla much reluctaaoe I take
up my pen to make the following remarks on this subject.
During the progress of the ' Synopsis of British Diatomacese,'
by the late Professor W. Smith, a frequent correspondence was
maintained between us, in which he constantly acknowledges
the value of my assistance in his investigations, and promised
to give me due credit for it in the work.
The difficulties attendant on a clear comprehension of the
structure of the frustule in the genera in question were considerable ; like nearly all the Diatomacese they are too minute
for actual dissection, and whilst very opaque dry, the appearances presented in. this state, so far as they could be made out.
MEMORANDA.
187
did not altogether harmonise readily with those in balsam.
Professor Smith, in several letters to me (May to October,
1853), expressed his inability to form clear conceptions of
their structure, and begged me to pay particular attention to
them, and try if I could make it out when engraving them.
At one time, in the course of correspondence, he writes, " I
do not quite understand your views;" at another, " I believe
you will prove eventually in the right."
The subject occupied my thoughts much, and many an
hour of patient labour was spent in the examination of specimens. A mounting of Rhabdonema arcuatum, burnt on talc,
dry, at length furnished me with the lpng sought for key to the
difficulty. Some of the frustules had been burst into their
components by expansion of the contained air, the pieces,
however, being left nearly in their relative position. Prom
this the analytical figure (f S. B. D./ pi. xxxviii, fig, 305f)
was engraved, and on receipt of the proof Professor Smith
expressed in warm terms his satisfaction with the result, and
as we laughed over it we wondered it could ever have appeared difficult. Had the briefest acknowledgment been mad®
in the ' Synopsis' that the discovery was mine I had been
amply repaid the trouble and time spent over it, and should
have been spared the very unpleasant task of writing as I
have felt obliged to. The appearance of the 3$cond volume of
the * Synopsis' without the promised acknowledgment pained
me much, but the friendship that had .existed between Professor Smith and myself prevented open mention of the injustice done me, on which, as I hope at a future day to write
on the Diatomacese, I should not have made the present
remarks, but that the subject was mentioned iij the last part
•of the 'Journal' in a manner which compels me to do so withAut further delay. The interesting specimen which furnished
the clue tp the jmjsteiy %% still jLu my possession, and I shall
be happy to show it to any who take an interest in the subject. Striatella, Tabellaria, Te,tracyclus, and Grammatophora, .after the .light thus taffpr.ded, W) Jogger presented any
difficulties.
It jras with great satisfaction I succeeded, 3#$ra?wch tja»e
:&ad patient .though^, dm resolving the .structure of J&hi
lenia, so nea% and pithily S c r i b e d by Mv- Brigh,tw
the last part of the ' Journal.' In the possession of "
.and iu. the indefinite increase of tkje frustule b f
division, this genus must undoubtedly in a n a t r
A g
\tjon be placed near Bhabdonewa, .fee. From p$ which,
however, it diffecs juj jthe inon-ppsse^sion of septa, in any of
tjhe several modifications now kppwn. The extreme obliquity
188
MEMORANDA.
of the sides of the incomplete annuli, forming, when in
juxtaposition, the zigzag appearance which first strikes the
attention of an observer directed to the Rhizosolenise, is no
bar to the accuracy of the proposed union, for it is only a
more developed state of a similar condition met with in
Striatella, as will be seen by reference to the figure of the
latter in the ' Synopsis B. D.,' vol. ii, pi. xxxix.
The advantages of burning Diatomacese on talc are hardly
yet sufficiently known or appreciated. In the more delicate
the use of this mode of investigation is especially apparent.
Viewed dry in this way, markings which balsam obliterates,
are then clear and sharp, but it is especially in the making
out of difficult points of structure, as we have just seen, and
the exact appreciation of minute differences between allied
species, that its value will be most felt.
Very pretty specimens of Diatoma, Grammatophora, and
the other forms of Diatomacese in which the frustules separate and cohere at alternate angles, have been obtained by
lightly burning specimens placed on the slide, over the flame
of a lamp. The admirable medium of Mr. Farrants promises, however, to render the preservation of such specimens
less difficult and uncertain. It will also, I expect, enable us
to mount permanently specimens in conjugation, which have
hitherto baffled every attempt made with this view, and if so
we may confidently hope, by the diffusion of such mountings,
to awaken further interest in this intricate subject.—TUFFEN
WEST, 8, Hemblington Cottages, Queen's Road, I>alston.
On the History of Arachnoidiscns.—In reply to your note
of this date I can say little beyond the fact that, on March
17th, 184-7 (just eleven years last Wednesday), 1 read a short
unscientific notice " On the occurrence of Arachnoidiscus
on an edible fucus from Japan," at the end of which, on a
question put by our friend John Quekett, I said, " From
the circumstance of these discs presenting a reticulated
appearance, similar to the webs of some species of spiders, I
propose to call the genus Arachnoidiscus, and the species
above mentioned Japonicus. My notice did not give a
scientific description of the genus intelligible to any one, and
therefore, as I have since learned, I have no claim to it. I t
might have been otherwise had any one kindly suggested to
my greenness the right course to render my notice of a new
thing perfect.
Dr. Walker-Arnott lately wrote to me on the subject at
the suggestion of Dr. Harvey, who knew what I had done,
and to whom I was indebted for species from Mauritius. He
MEMORANDA.
189
wished to know who was the author of the genus, and where
Bailey's description was to be found, &c.; and I sent him a
copy of my notice. Bailey gets the credit, perhaps properly
according to rule, but I cannot help feeling—waiving my
having suggested the name—that Shadbolt has the prior
claim, as he read a paper on the subject, November 14th,
1849 ('Trans. Micr. Soc./ vol. iii, p. 49). I have an impression that the first specimens Bailey ever had were mine,
forwarded to him by Mr. Marshall, who I am sure would
have named to him the whole history. A matter of this kind
is so trivial and insignificant, that it is not worth discussion
except on principle, and I cannot help thinking that it would
be well if men advanced in scientific knowledge, and holding
a deservedly high position in consequence, would encourage
the smaller fry, by giving them every credit for their small
but earnest labours and good intentions in the common
cause.
I suspect Mr. Tuffen West has done more with this genus
than any other man in this country.
At the time I wrote my notice all the Diatomacese were
generally presumed to be animal, their anatomical structure
was little known and seldom was any given, the name being
supposed to convey a tolerably correct idea of the object.—
HY. DEANE, Clapham Common.
Physical Influences exerted by living Organic and Inorganic
Membranes upon Chemical Substances.—In a paper published
in the ' American Journal of the Medical Sciences/ by Mr.
Joseph Jones, he gives the following results of a series of
experiments upon living animals and plants.
" 1. Cell-walls, like animal membranes, exert a physical
influence upon the chemical substances held in solution passing through them. This physical influence is capable of
altering the arrangement of the molecules of the precipitate
formed within the cells, so that the precipitate which under
ordinary circumstances consists of irregular granules, under
the influence of the endosmotic action assumes a regular
crystalline form.
" 2. The cells of different vegetables, like different animal
membranes, change in different manners the arrangement
of the molecules of the same substance.
" It may yet be demonstrated, by experiment, that cells in
the same plant, having different offices, elaborating different
products, exert a different physical influence upon the same
chemical substance. Or, in other words, the crystalline
deposit of the same substance will vary in physical properties
with different cells."