230 LILIAN SHELDON. 



divided up into a number of rounded segments, which, however, 

 bear no relation to the true segmentation. 



5. The protoplasm is in the form of a reticulum, and there 

 are no traces of cell outlines. 



6. In the next stage, which I have examined after the segmen- 

 tation, there is a specially marked area of reticulate protoplasm, 

 containing a large number of nuclei extending through about 

 one third of the length of the ovum, and having in transverse 

 section an irregular triangular shape, the base of the triangle 

 resting on the surface of the egg. Nuclei are present through- 

 out the whole of the yolk, being more numerous at the 

 periphery than at the centre. 



7. The triangular-shaped protoplasmic area becomes more 

 compact and flattens itself out, forming a plate-like mass of 

 protoplasm densely packed with nuclei on the surface of the 

 egg. Its lateral edges turn slightly inwards away from the 

 periphery. The nuclei over the rest of the egg have undergone 

 no change. 



8. The embryo is present as a closed sac, the walls of which 

 are separated from the vitelline membrane by a thick layer of 

 yolk, in which small round, highly refractive bodies are present. 

 The embryo is enclosed in a thin layer of protoplasm, with 

 nuclei, which represents the ectoderm. Along one line, in a 

 longitudinal direction, there is a prominent ridge on the outer 

 side of the ectoderm, composed of proliferating nuclei. Ante- 

 riorly this ridge divides into two, which remain attached to one 

 another above and below, in such a way as to enclose a cavity 

 between them. 



9. At the next stage the rudiments of the prseoral lobes are 

 present in the form of a thickened mass of cells at the ventro- 

 lateral corners of the embryo. At a very short distance from the 

 anterior end of the embryo the yolk is divided by a protoplasmic 

 septum, which runs in a longitudinal horizontal direction, 

 and separates the body of the embryo into two sacs, one lying 

 above the other. The septum stops short at a short distance 

 from the posterior end, so that the two sacs communicate freely 

 round its end. At the regions where the septum joins the body 



