conferred upon sucli forms by the presence of these accessory
methods of attachment and adhesion ; while the filamentous
species, being usually aggregated in considerable masses, or
entangled amidst the branches of the larger Algæ, are also less
liable to dispersion.
From an examination of the figures referred to in the above
list, it will be seen that while the general character of the
process, which consists in the intermingling of the endochrome
or cell-contents of the parent frustules, is the same throughout,
there are pecidiarities attending the process in the different
genera which prevent us from giving a detailed description
of the phænomena that will apply to every case. The most
notable of these peculiarities are the variations in the number
of the conjugating frustules and the sporangia which result from
the process. These variations may be reduced to four classes.
I. We have two parent frustules and two sporangia as the
result of their conjugation. This mode is seen in Epithemia,
Cocconema, Gomphonema, Encyonema, and CoUetonema.
II. From the conjugation of two parent frustules we have a
single sporangium. This occurs in Himantidiim.
III. The valves of a single frustule separate, the contents set
free rapidly increase in bulk, and finally become condensed into
a single sporangium. This may be seen in Cocconeis *, Cyclotella,
Melosira, Orthosira, and Schizonema.
* I have not attempted to reduce the examples of conjugation given by
Dr. GritSth and Mr. Carter to any of the above classes. In the details and
figures of these writers there are circumstances which I cannot explain in
accordance with the known phænomena attending conjugation in other cases,
and the significance of which I cannot comprehend without a personal examination
of specimens.
Judging from the figures given by Dr. Griffith of the conjugation of
Navícula, I should refer that genus to the third mode I have mentioned ; hut
the text of Dr. Griffith’s paper, speaking of “ parent frustules,” would point
to my second mode as the process he had observed. The “ rugose siliceous
sheath ” enveloping the sporangium, as described by Dr. Griffith, I have
never observed ; probably it may have been an appearance resulting from the
condensation and corrugation of the mucus developed around the reproductive
body. If the figure given in the ‘ Micrographie Dictionary ’ of the conjugation
of Surirella be correct, that genus will also fall under my second class.
In Mr. Carter’s paper, the formation of two sporangia in Cymbella and
In Melosira nummuloides, M. Borrerii, and M. subjlexilis, the
second valve of the conjugating frustule is rarely found united
to the mucus surrounding the sporangium, the conjugation
taking place only in the last frustule of the filament; but in
Melosira varians and Orthosira orichalcea, conjugation taking
place throughout the entire filament, both valves are usually
found adherent to the sporangium or its surrounding mucus.
IV. From a single frustule, as in the last method, two sporangia
are produced in the process of conjugation; this takes
place in Achnanthes and Bhabdonema.
However varied these methods may appear on a superficial
view of the conjugating process, they will not, on a further consideration
of the nature of these organisms, be found to involve
any physiological diversities.
We have already remarked, that, “ during the healthy life of
the Diatom, self-division is being continually repeated (Introd.
vol. i. p. xxv); while the frustule is performing the simple
functions of its life and growth, its contents are therefore being
continually submitted to the separative process which precedes
the self-dividing act. The functions of life and growth are not
suspended during the act of conjugation, and in consequence
self-division may take place at any stage of the process which
accompanies the formation of the reproductive body; or the
latter process may intrude upon, or arrest any step in the
progress of self-division.
In the first mode of conjugation, as occurring in Epithemia,
&c., self-division may be regarded as in the earliest stage of its
Amphora is represented as the result of the conjugation of two frustules;
these genera must therefore be referred to my first class. The conjugation of
Cocconeis is described as similar to the others, hut two of the figures given,
viz. figs. 5 & 6, harmonize the process with that noticed by myself in the
same genus.
The circumstance dwelt upon by Mr. Carter as having an important bearing
upon the rationale of the process, viz. that one of the conjugating frustules is
invariably smaller than the other, is altogether at variance with my experience,
and is totally irreconcilable with the process as it occurs in the genera mentioned
under my third and fourth classes. I am therefore disposed to believe
that the difference in size noticed by Mr. Carter was a mere accidental diversity,
and of no essential signification.