158 Proceedings of the Royal Physical Society. 
of the single or conjugated Gregarina bursts, and the pseudo- 
naviculEe escaping, presently give vent to amoebiform bodies, 
which are at length developed into Gregarina. The con- 
sideration yet remains , — must the so-called nucleus be con- 
sidered as an ovary or a true ovum ? I am disposed to view 
it as the latter, on account of the existence of the single 
nucleolus and spot within it, and to consider the so-called 
polymorphic development as comparable to the fissure stage 
in the ova of higher animasl, but which, in the case of the 
unicellular Gregarina and Ehizopod, becomes a final stage 
of egg development ; and I would hint, that in the higher 
animals the fissured elements of the ovum remain together 
to form a multicellular organism, while in these lower ones 
the same elements finally separate at a corresponding stage, 
to form a swarm of unicellular animals. 
2. On the Sting-Cells o/Cydippe. 
In Agassiz's contribution to the " Natural History of the 
United States," vol. iii. p. 238, a description is contained of 
the thread-cells of Cydippe, which purports to be a more 
correct account than that given by Gegenbaur and myself. 
The author states the cell contains a spiral thread, as stated 
by us, but he also states that the granular matter which we 
had described as within the cell is really without it, and 
consists of a close layer of granules investing the whole 
wall of the cell. Now it is very evident that, in case the 
cell were covered with a simple layer of granules, it would 
be impossible that it could retain its hold of the wall of the 
tentacle, and would also difi*erfrom the mode of attachment 
of the thread-cells of all other animals, which, however 
they may vary in structure, are always buried in the ecto- 
derm of the structure in which they are situated. On a 
re-examination of these bodies, I found that Agassiz was 
correct in his opinion as to the granular matters being 
situated in the exterior of the cell, but mistaken in his 
opinion that it merely consisted of a layer of granules at- 
tached to the cell. The whole tentacle is, in fact, covered 
with an ectoderm of sarcode, which, like that of Actinophrys, 
