DUBLIN UNIVERSITY ZOOLOGICAL AND BOTANICAL ASSOCIATION. 249 
form species also to present a central division of the endochrome, which 
is also of a contracted waved outline, enclosing a central series of cor¬ 
puscles similarly to Docidium asperum (.Breb .), and to the first noticed 
species. In this species I have also noticed indications of the same 
mode of division as described and figured in the first form. There is 
no perceptible gelatinous sheath, so far as I can make out, surrounding 
any of these three organisms. I regret I have not been fortunate enough 
to meet with the reproductive state of any of them. If I might ven¬ 
ture on a conjecture, I should probably say that it takes place by con¬ 
jugation of the separated joints. 
It will be by this time seen that the end at which I aim is to indi¬ 
cate that I think the first-described organism, D. asperum (Breb.), and 
the fusiform species, belong to the same genus. It is true I nave not 
been able to see moving granules at the extremities of Docidium asperum 
(Breb.) nor of the fusiform species, although, on the authority of Mr. 
Balfs, it is stated that M. de Brebisson has seen them in the former. For 
my part, I do not doubt that they may exist, for it seems to me that 
the rather opaque asperities which cover the surface of the joints may 
hinder them being noticed. I have sometimes thought I saw them, but 
could never feel positive. In any case I might remark that we have 
species of Penium both with and without active granules. 
Assuming it as granted that these three forms belong to the same 
genus, it may be thought necessary to inquire, is that genus Docidium ? 
I do not think so. In the first place, all these species entirely want any 
constriction at the centre of the joints, nor are the segments at all di¬ 
lated at the base; both which are, as it appears to me, essential cha¬ 
racters of Docidium, and which are very manifest in all the British 
species, as well as in the American, as figured in Balfs. This, I admit, 
however, must be stated with one slight exception, for here I am not 
unmindful of Docidium minutum (Rolfs). In that species there appears 
a distinct central constriction, but there is no evident inflation at the base 
of the segments. There appears a terminal, well-defined cavity in which 
are moving granules, not as in the first of the new forms which I now 
bring to notice, a space, left merely by the withdrawal of the endochrome, 
in which these move. Moreover, Docidium minutum is not a filamentous 
form. Mr. Balfs himself allows Docidium asperum (Breb.) to remain 
in that genus unwillingly, and merely because he had no better course 
open. But perhaps it might possibly by some be urged that the es¬ 
sential characters of the genus Docidium might with propriety be altered 
by omitting those before mentioned, which seem to be abundantly suf¬ 
ficient to exclude the three forms in question; or some might say they 
might be kept in Docidium as aberrant members of the genus. It occurs 
to me that the answer to such suggestion is found in the fact of these 
three forms being filamentous ; else we might with as great propriety 
and as good reason include, for instance, Sphserozosma with Cosmarium, 
or Desmidium with Staurastrum, the separated joints of which filamen¬ 
tous genera resemble the free genera Cosmarium and Staurastrum re¬ 
spectively, more than do the separated joints of the filamentous forms 
