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tlieir very elegant and beautiful appearance under the micro-
scojio. IMnch of the beauty of those most interesting of all
Nature’s works, the Zoophytes, arises from the same cause.
Connecting the zoosjiores with each other, we find in most
of the Conferva a vascular structure. (See PI. 17.) In the
genera Vesiculfera, Zygnema, Microspora*, and doubtless
in many other Alga, the zoospores up to a certain period
of the developement are connected with each other, and
probably with the central cytoblast, hy means of a tubular or
vascular network, in the angles formed by which the zoospores
are situated. This structure is most manifest in Conferva
crispata and its allies, and requires, in order tha t it may be
clearly seen, tha t the developement of the species should be
considerably advanced, and the zoospores somewhat scattered.
I t may generally, however, be easily detected in the genera
Vesiculifera and Zygnema. In the latter the tubular formation
is not arranged in a reticulated manner, bu t occupies the
centre of each spiral thread. I t is by the inosculation of the
tubular radii given off by the central cytoblast with this
vascular structure, tha t a direct communication is established
between that organ and the zoospores, f
In addition to the membranes above described, the zoospores,
Avith the vascular netAvork, the sporangia, and the central cytoblast,
tAA’O other organs have been noticed in the Conferva,
first by Mr. Bowerbank in a species of Zygnema, which I
transmitted to him, and subsequently by myself in a variety
of other species. The one is cruciform and adherent to the
interior wall of the cell. (See PL 17. fig. 1, 2, 3.) I t (Mr.
BoAverbank remarks) “ is the vegetable structure which
secretes the raphides.” They are probably not definite organs,
but crystals. The other body is small, elongated, somewhat
curved, and attached to, or lying upon, the plant. (See PI. 17.
fig. 1,2,3.) This (Mr. Bowerbank observes) Is certainly “ a
string of minute cytoblasts; and similar bodies, but more
* Cladophora Kutzing.
f See “ Annals and Magazine of Natural History,” vol. xii. p. 20., for a
paper entitled, “ Observations on some Points in the Anatomy and Physiology
of the FreshAvater ConfervEe.”
curved, are observed in the soft parts of the young lips of
shells, both marine and freshAvatcr.” Several of each of these
organs may be found in each cell.
All the separate and distinct structures and parts entering
into the formation of the Conferva have now been treated o f :
certain peculiar adaptations and contrivances still remain to be
described, such as the InA’ersion of the extremities of the cells
in many Zygnemata, the corrugated cells of the Vinculifera,
the layer o f fibres surrounding the main stems of some
Batrachosperms, the ciliary processes met Avith in the same
genus and others nearly allied, and the presence of silex in
some Diatomacea. The further notice of these, hoAvever, Avill
he postponed until the individual genera come under consideration.
The rapidity of the growth of Conferva, and indeed of all
the articulated Alga, has often been a subject of surprise to
many observers of N a tu re ; and to none more than myself has
it occasioned greater astonishment, until I became acquainted
• with the reason of so surprising a developement of structure.
I f the filaments of Zygnema, nitidum be carefully examined
and contrasted together, it Avill be seen tha t in some the
length of the cells only ju st exceeds their diameter, and that
each cell usually contains four spiral coils, which together
perform from seven to eight turns in each, the coils almost
touching each other : that In other filaments the length of the
cells is more than three times the diameter, but that still each
cell contains only the same number of revolutions of the
spires, viz. seven or eight, which noAV, instead of being nearly
in opposition, are widely separated; thus plainly proving the
elongated cells to be derived from the extension of the
shorter ones. And again it will be noticed in other filaments,
that the cells have returned to their original length, but that
each now contains only three or four spiral turns, thus
affording manifest proof of the division of the elongated
cells, and completing the chain of evidence which establishes
to demonstration the existence of the modes of growth to
which I have referred throughout all the cells in the species
of the genus Zygnema. The proofs now to be adduced, that