474 R. M. PACE. 



wLicli tlie sectiun is taken. ¥i^. 9. — A &ectiuu of the egg bliowing the 

 commencenient of the clear region in which tlie yolk-nucleus generally lies. 

 In Fig. 10 the section passes through the nucleus and nucleolus, and the 

 clear space has assumed a hemispherical shape. In Fig. II the yolk-nucleus 

 is shown as a well-developed crescentic body lying in the clear space visible 

 in the preceding figures, and in close contact with the germinal vesicle ; the 

 section passes through only the upper part of the nucleus. Fig. 12. — The 

 yolk nucleus is seen lying in a clear space. Tlie germinal vesicle is no longer 

 visible, but lies underneath the cap formed by the yolk nucleus, x 400. 



Fig. 13. — A section of an ovum of about the same age as that illustrated 

 in the preceding figures. The yolk nucleus has become rather more crescentic 

 in form, and three large vacuoles are present and contain crystalloid bodies 

 (<?;•.). X 400. 



Fig. 14. — A section of an egg of the same age as that shown in fig. 10. 

 The yolk nucleus is more markedly hemispherical in form, and the number of 

 vacuoles is larger than at previous stages. X 400. 



Fig. 15. — Section of an older egg. The yolk nucleus has now assumed the 

 form of a ring surrounding, and in close contact with tlie germinal vesicle. An 

 indication of approaching degeneration is seen in the reticulate structure of 

 the yolk nucleus, x 400. 



Fig. 16. — A section of a still older egg in which the degeneration of the 

 yolk nucleus has commenced. The yolk nucleus has lost its regular outlinc> 

 and shows a markedly reticulate structure, the meshes of the network staining 

 more deeply than the interlying substance. 'J'he outlines of the surrounding 

 space have also become somewhat irregular, x 400. 



Fig. 17. — A section of an egg at a slightly later stage. Tiic degeneration 

 of the yolk nucleus has advanced considerably and is very marked. The body 

 has completely lost its regular outline, and the boundary of the surrounding 

 space is very irregular. X 400. 



Fig. 18. — Section of au older egg, showing the complete disintegration of 

 tlie yolk nucleus, which has now assumed the form of numerous minute, 

 darkly-staining granules which lie in a loose ring around the germinal vesicle 

 X 400. 



Fig. 19, — Section of an egg of about the same age as that shown in 

 fi"-. 18, but which exhibits a somewhat different method of fragnicutation ol 

 the yolk nucleus. In this case the products of disintegration have assumed 

 the form of dark, irregular patches lying within clear spaces, and forming an 

 open ring around the germinal vesicle. X 400. 



Figs. 20, 21. — Sections of eggs showing still other methods of fragmenta- 

 tion of the yolk nucleus. X 400. 



