No. 2.] EMBRYOLOGY OF THE AMERICAN LOBSTER. 22J 



They are most abundant around the periphery, and when viewed 

 under a high power (PI. XVI, Fig. 8) are found to be embodied 

 in amoeboid masses of protoplasm. 



The clear layer already noted is in section found to form a 

 lenticular mass (Fig. I, l.m.), which, by the use of high powers, 

 may be resolved into fine grains. Its edges are seen to pass 

 into the peripheral layer of the remainder of the egg. The 

 delicate primary egg membrane encloses the whole. 



Before considering the egg after extrusion, it may be well to 

 compare further the ovarian egg of Homarns with that of related 

 Crustacea : — 



Waldeyer ('70), describing the ovary of Astacus, speaks in a 

 general way of the epithelial origin of the egg, a view that is 

 now most universally adopted. He also calls attention to the 

 follicles; to the "vitelline membrane"; to the clear, fine-grained 

 perivitelline layer ; to the increase in size of the yolk spheres 

 towards the centre ; to the large germinal vesicle, and to the 

 germinal spot. 



The origin of the egg of Atyephira from indifferent ovarian 

 cells is almost precisely like that of Homarus ; and Ishikawa 

 ('85) also describes the presence of more than one germinal 

 spot in the youngest egg-cells, and the presence of vacuoles — 

 which, however, are larger, and appear earlier, than in Homarus. 

 As regards structure and relative size, the germinal vesicles of 

 AtyepJiira, Eupagurus, and Homarus are almost identical, as is 

 also the final excess of yolk matter over protoplasmic. 



The radiating strands of protoplasm described by Mayer, 

 though absent in the younger egg-cells, are present at ovarian 

 maturity. 



There is nothing to show that the yolk does not originate 

 endogenously. 



Though in AtyepJiira and Eupagurus the primordial vesicle 

 is said to disappear while the eggs are still within the ovary, 

 leaving the egg a "cytode," I have examined many eggs lying 

 free in the ovary, and have not yet found a single one without 

 a nucleus. The earliest external eggs that I have been able to 

 find, though invariably nucleated, have the much smaller nuclei 

 of segmentation. Absolutely fresh eggs I have been unable to 

 secure ; for a lobster in the act of ovipositing has yet to be 

 found. 



