158 Proceedings of the Royal Physical Society. 



of the single or conjugated Gregarina bursts, and the pseudo- 

 naviculse 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 Khizopod, 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 of 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 differ from 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, 



