joufS MlS^'mT ^oyal Microscopical Societij. 275 
There are two forms of cells which seem to supply connecting 
links between Fig. 10 and the fully-grown zoosperms (Fig. 12), 
these are cells whose nuclei are more consolidated and firmer than 
those of the cells which have as yet been under consideration ; they 
refract the light considerably, and have a spot in the centre sur- 
rounded by a dark circle; the other forms are triangular and 
present all the appearance of the heads of zoosperms, than which 
they are rather larger, the spot in the centre of these is dark, the 
line round having become triangular. 
The interpretation I am inclined to place on the above series of 
facts is that the zoosperms are derived from the cells with smooth 
nuclei, which gradually diminish in size, and at the same time 
increase in consistence, until they are transformed into mature 
zoosperms ; the nucleus appears to form the head, the remainder 
of the cell becoming the tail and rays, so that no part of the 
zoosperm is formed within a cell membrane. On this view I 
confess that I do not see how the larger cells are concerned in the 
process ; they are too large to be consolidated into zoosperms direct, 
for if that were the case, the smaller cells would be of a greater 
consistence and larger size than they are actually found to be. I 
think it more probable that they become transformed into the 
latter by cell division, an idea which is rendered more likely by 
the fact, that there is every gradation of size between one form of 
cell and the other. 
According to KoUiker,* it is the nucleus which forms the tail, 
while the rest of the cell forms the head; but in a subsequent 
paper, t in which he abandons his former opinion concerning the 
development of zoosperms in favour of the doctrine that they arise 
entirely from the nucleus, he considers that all these motionless 
zoosperms are only altered nuclei. My researches do not counte- 
nance either view, the presence of both nucleus and cell substance 
disproving the latter, and the gradual consolidation of the nucleus 
making the former view untenable. 
I have every reason to believe that the process of development 
is substantially the same in all the species examined; the sperm 
cells of 8. Longirostris (Fig. 13) differ only from those of P. Bern- 
hardus, in having fewer, but larger granules scattered through their 
substance ; the amount of change required to transform them into 
mature zoosperms would be less than in the latter species. 
In the lobster (Fig. 14) the sperm-cells have very large nuclei, 
whose appearance is more like a vesicle than in P. Bernhardus ; 
their contents are very granular, there are present smaller cells, 
with the nucleoid body external, resembling the corresponding 
cells in P. Bernhardus, but exceeding them in size, as would be 
expected, from the larger size of the zoosperms in the lobster. 
* Loc. cit. t ' Zeit. f. wiss. Zoologie,' Bd. 7. 
