of the Bay of Naples. 97 



in wliicli numerous solid nuclei of different sizes are scattered. 

 The three nuclei situated in the following section approach 

 the ordinary form, which we see in the next section, by the 

 possession of a nucleolus, although this is but small. ^ The 

 only remarkable deviation presented by the third section is that 

 its plasma is not yet segregated around all the nuclei into sepa- 

 rate ova. The ovary placed on the other side of the body in 

 the same individual, on the contrary, showed nothing but dis- 

 tinct ova with nuclei of the usual form. One cell con- 

 taining a remarkably large nucleus, appeared to be in process 

 of division, at least the form of the nucleus and an annular 

 constriction of the plasma led to this conclusion. The first sec- 

 tion of the left ovary seems to indicate that the ova at first are 

 not sharply separated from each other, but owe their origin to 

 a germinal layer, and that a transformation of the nuclei goes 

 on side by side with the development of separate ova. _ Per- 

 haps, however, such a germinal layer does not occur in all 

 individuals, but only in such as have left the egg compara- 

 tively early ; at least, I have met with many young females 

 in the ovaries of which all the ova were distinctly separated 

 from each other. It must remain for future investigations to 

 clear up completely the genesis of the female sexual products. 

 In the developed ovary we do not always observe the con- 

 trast above-mentioned between aggregations of ova rich and 

 poor in vitellus, but frequently all the cells are of the same 

 structure. 



The extruded ova are of very considerable size in proportion 

 to the mother, and have an oval form pointed at one end 

 (fig. 10). Their length is about 0'187 raillim., with a maxi- 

 mum breadth of 0'06 millim. It is remarkable that the true 

 ovum, the vitelline mass, only fills a little more than half 

 of the cavity enclosed by the structureless egg-capsule, the 

 rest of the space being occupied by a limpid fluid. In this I 

 always found one or two rounded polar corpuscles of 

 0-007-0-015 millim. in diameter; these break up very slowly, 

 so that we still find them with fully developed embryos. As 

 a rule, only one polar corpuscle with a distinct nucleus was 

 present, and this always lay in the fluid of the pointed half 

 of the ovum ; if a second had been formed it was always of 

 smaller size. Only when the embryo approaches the end of 

 its period of development it becomes so voluminous that it 

 nearly fills the egg-capsule, even when, as appears to be 

 always the case, the head and tail are folded up against the 

 trunk. Owing to the abundance of yolk in the Qgg^ it was 

 impossible for me to ascertain the details of the development. 

 The newly-hatched animals are about 0-39 millim. long and 



Ann. & Mag. N. Hist. Ser. 6. Vol. ii. 7 



