conveyed, by means of tlie tubular radii, to those organs by
which the materials are to he assimilated.
The cytoblast, therefore, is at first fixed in the centre of
the cell by the prolongations which proceed from it ; b u t it
liappcns, that at a certain epoch these radii disappear, and
then the cytoblast floats freely within the cavity of the cell ;
the disappearance of the rays, the cessation of the growth of
the cells, and the assumption of the characters of reproduction
being almost contemporaneous, or, at any rate, events immediately
consecutive on each other, and the two latter being
readily accounted for by the disappearance of the radii.
The circumstance of the increased developement of the
cytohlastic body subsequent to the removal of the radii, gives
^veight, to the opinion th a t this organ has yet another office
to perform, in addition to that of presiding over the growth
of the cells ; for were it not so, it might be expected tha t on
the disappearance of the rays it would shrivel up, and at
length become absorbed, as is the case with other organs,
tlieir allotted duties having been performed : and the office
Avhich I would attribute to it, is one even of more importance
than that previously remarked upon, it being no other than
the fertilization of the brilliant granules entering into the
formation of the spiral threads, and which I regard, as before
noticed, as the unfertilized zoospores.
The adoption of the vicAV which supposes the fertilization
of the reproductive bodies by means of the organ whose
complicated anatomy has been dwelt upon, would have the
effect of removing some grand difficulties in the way of the
complete understanding of these most interesting productions.
Thus, first, by furnishing a definite organ whereby fertilization
is occasioned, it removes the inability which has hitherto
been felt to explain in what way the intermingling of bodies,
in all respects so similar in organization and appearance as
the bright granules of the Conferva seem to be, can be regarded
as giving origin to fertility : secondly, it does away
with the anomaly, which has always appeared to me so strange,
that a combination of the matter of two cells should invariably
take place in certain divisions of the Confervoid tribe of
productions ; while in other divisions of the same tribe, which
could not bo supposed to differ fundamentally froin the
former, no such phenomenon has hitherto been recognized ;
by shewing that this combination is not an essential to the
perpetuation of the species : and thirdly, it explains the permanence
of species which have perished before union of the
endochrome and formation of spores have taken place.
I have detected cytoblasts in numerous Zygnemata, but
the best species in which to examine them are the larger
kinds, such as Zygnema maximum, Z . nitidum, and Z. belle.
Of the genus Vesiculifera, I have also found it in several
species : they cannot always he seen in these, owing to the
cells not being so transparent. I doubt not, however, hut
tha t they are general in it, as well as other genera of Alga,
whether marine or freshwater. I n this genus ^ it is but a
simple vesicle ; at least, I have never observed it in any other
state. (See Plate 17. f g . 6.)
The Eev. M. J . Berkeley has kindly favoured me with an
abstract of a paper by Hugo Mohl on the genus Antlioceros,
published in 1839, and inserted in “ Linnæa,” vol. xiii. p. 273.,
ill the cells of which an organ occurs bearing a considerable
external resemblance to the radiated structure met with in
the cells of Zygnema.
The following is a brief outline of the mode of formation
of this structure in the genus Anthoceros. "Wlien an immature
cell of one of the species of this genus is examined, a
portion of its interior is seen to he occupied by a layer of
green granules, through which may be seen a cytoblast, the
other portion of the cell being colourless. Treated with
iodine, the layer formed by green granules, as also the colourless
part of the cell, becomes yellow, showing that the whole
is really lined with a sort of quasi membrane. Gradually the
green layer becomes concentrated into two masses, which
commence to advance more and more towards the mddle of
the eells, and the edges of these masses spreading in various
degrees over the inner wall of the cell, leave intervals of
various sizes, which give to them a cellular appearance.
“ The nucleus, or cytoblast,” Mohl observes, “ has no part in
B 4