I'late V. 

 Fig. 49. Section of a four-cell stage, showing small yolk grannies at the 

 animal pole and the relative extent of the first and second cleavage planes. 



X 13. 



Fig. 50. Section through an eight-cell stage showing partly segmented lower 

 mass of yolk and rather large segmentation cavity. X 13. 



Fig. 51. Section of a few-cell blastula stage such as shown in surface view 

 in Figs. 21, 22 and 23, PI. II. In this stage the cells with small granules of 

 yolk have divided a number of times, but the larger mass of the egg is only 

 partly divided by external cleavages, x 13- 



Fig. 52. Section of a many-cell blastula, such as shown in Figs. 2() and 27. 

 I'l. III. X 13. 



Fig. 53. Section through a small portion of the vegetative i)ole of an egg 

 in a slightly earlier stage than that shown in Fig. 51, or about the stage 

 shown in Fig. 25, PI. III. In this stage the surface of the egg seems to indi- 

 cate a total division of all parts into blastomeres, but this section shows that 

 the central mass of yolk has not yet become segmented, x "47. 



Fig. 54. Section of a later stage than Fig. 52, no segmentation cavity, a 

 large portion of the central yolk cells surrounded by smaller cells, and in one 

 place there is a considerable down-growth of these smaller cells into the 

 larger yolk cells. This is a section of the blastopore stage shown in Fig. 28, 

 PI. III. X 13. 



Fig. 55. Enlarged portion of the invagination shown in Fig. 28, PI. III. 

 X55. 



Fig. 50. Bimch of eggs photographed luuler water. 



Fig. 57. Photograph of later stages of embryos with yolk sac attached. 



