110 MALCOLM LAURIE. 



granular^ the rest of the space being filled up with the larger 

 spheres. 



The nucleus (fig. 4, n.), which retains its central position, 

 is large ("05 mm.) but indistinct in outline and is probably- 

 breaking down as I have been unable to find any trace of 

 it in eggs larger than that here figured. The nucleolus 

 (fig. 4, n' .), which is situated towards one side of the nucleus, is 

 also large, staining darkly with carmine and showing a very 

 distinct circular outline. It often contains one large, clear, 

 circular vesicle and a number of smaller ones. 



The whole egg is surrounded by a distinct, rather thick 

 vitelline membrane (fig. 4, v. m.). No trace of poi'es or any 

 other structure was made out. Outside the vitelline membrane 

 the egg is surrounded, except at the base, by the follicle in 

 which the two layers {fol. and fol'.) of the ovarian tube can 

 still be traced. The cells of the inner layer of the follicle are 

 now flattened and small. The large yolk-forming cells at the 

 base of the egg [ger' .) have increased in size and arranged 

 themselves in a circle the centre of which is occupied by a 

 prolongation of the ovarian tube (mi). The egg is only 

 separated from this prolongation of the lumen by the vitelline 

 membrane. The spermatozoa are thus enabled to reach and 

 fertilize the egg while it is still in its follicle. 



PI. XIII, fig. 5, shows the base of a ripe egg attached to the 

 ovarian tube. The pedicle has become shortened and its lumen 

 has increased very much in size. The yolk-forming cells have 

 degenerated, their flattened nuclei {ger'.) being, howevdl", still 

 distinguishable, and the follicle has become much thinner owing 

 to the growth of the egg. The egg itself is a mass of tightly 

 compressed yolk-spheres, among which I have in vain sought 

 for the nucleus. It is probable, however, that the nucleus and 

 the greater part of the protoplasm migrate to the base of the 

 egg as segmentation commences there. 



The yolk (PI. XIII, fig. 6) consists of spheres, ranging up to 

 •2 mm. in diameter. They are not homogeneous, but contain 

 spherical or prismatic bodies, which stain darkly with borax 

 carmine. These bodies are very large in the smaller yolk- 



