exact similarity of the contents of the different cells, — no
difference being detected, even with the assistance of the most
powerful glasses, — and the principal mode of growth of the
Conferva, by the extension and repeated sub-division of the
primary cell,— would tend to lead likewise to a similar conclusion.
Notwithstanding the difficulties Avhich lie in the Avay of
regarding each cell of a Conferva as the representative of a
sex, the frequency with which the phenomenon of union of
the filaments, and commixture of the contents of tAvo cells,
takes place, cannot be regarded otherwise than as most
curious, though the purpose to Avhich it is subservient is so
obscure. I t may be, tha t it merely serves to bring a number
of the reproductive granules into contact, and which, becoming
subsequently clothed with a membrane, are thus the better
preserved until the proper time for their germination arrives.
Another circumstance opposed to the sexual vicAV as regards
distinct cells, is that, in those genera even in which
either the cells or their contents unite, exceptions occur in
which there is an absence of conjugation of the filaments,
and commingling of endoclirome or vesicular contents of the
cells ; and in other cases there is conjugation, but no mixture
of the endoclirome of the united cells.
Thus, so far as can be presumed, the information already
acquired would appear to be opposed to the belief in the
existence of sexes as applied to cells in the Conferva. A fertilization
of the sporules does doubtless occur ; and this I
believe to be effected through the agency of the following
structure, described, nearly as below, in the “ Annals of Natural
History,” vol. xii. p. 20. In this description it will be seen
th a t a double office has been attributed to i t ; I am now
induced to limit its use to the one, the important one, of
fertilization.
From the high developement of the cells of many Alga,
both marine and freshwater, as well as from their extreme
transparency, in many species, it might have been supposed
tha t the first discovery of those curious organs, termed cyto-
blasts, Avhich exercise an influence so mysterious on the developcment
of cells, and whose presence in cellular structure
is so constant as to lead to the suspicion tha t the association
of the two organisms is universal, would have been made in
this extensive tribe of Nature’s wondrous works; so far, however
from this being the case, they have not as yet, so far
as I can learn, been noticed in any species of A lg a ; a
description of them, therefore, as they occur in two genera of
freshwater Conferva, Zygnema and Vesiculifera, cannot fail
to be of interest.
In the first of these genera, Zygnema, their structure is
exceedingly complicated.* Each cytoblast is solitary, and
usually occupies a central situation in each cell of a Zygnema.
I t consists generally of two membranes, but sometimes
there are th re e ; the innermost of these being either circidar
or elliptical, (the form varying with the species itself, as well
as its condition,) and presenting a nucleated appearance; and
all are separated from each other by distinct intervals, which
are filled Avith fluid. The surface of the enclosed membrane
or membranes is smooth; while tha t of the external is rendered
irregular by the giving off of numerous tubular prolongations
or radii, which terminate in the spiral threads
formed by mucus, eudochrome, and large bright granules,
which I regard as the unfertilized zoospores.
Wishing to have a corroboration of my views respecting
the structure of the cytohlastic organ described above, and also
to learn as much respecting its anatomy as possible, I forwarded
a specimen of Zygnema nitidum to tha t able and most
obliging observer, J . S. Bowerbank, Esq., whose opinion of
its structure exactly coincides with my own, tha t gentleman
having in particular satisfied himself of the tubular nature of
the prolongations sent off by the external membrane, and of
their termination in the spiral threads.
The structure of this curious organ explains with apparent
satisfaction one of the offices which it is destined to discharge,
viz., that of a laboratory or stomach, in which the materials
necessary for the growth and vitality of the cell and its con*
tents are received and digested, and from which they are
* See Plate A -fig . 1, 2 3.
B 3