No. I.] POLYCHOERUS CAUDATUS. 165 



after D and D' , E and E have divided, they invariably give 

 rise to B\, Bz, B'l and ^'2 respectively, as is shown in Fig. 10. 

 This figure shows the pigment granules dividing the cell B into 

 approximately equal parts, and the plane of cleavage follows 

 this line. Occasionally the line of granules and cleavage plane 

 is somewhat oblique to the line as represented in this figure, 

 and in such cases a rotation takes place, so that eventually the 

 cells Bi and Bz lie as is shown in Figs. 15 and 20. The cells 

 B'l and B'z are derived from B' in an exactly similar manner, 

 and lie on the side of the ovum opposite to that drawn. At 

 about the same time B^ and B't, are budded off from B2 and 

 B'2 respectively. 



The cells D and D' are generally the next ones to divide. 

 Figs. 8 and 10 show the cell D from the side, and Fig. 11 

 shows both D and D' from above. The division takes place, as 

 is shown in Fig. 13, along the long axis of the ovum, thus 

 giving rise to Dr, Dl, Dr, D'l. Also C and C divide in a 

 similar manner (Fig. 13), giving rise to Cr, CI, Or, C'l. At 

 about the same time as this takes place, E and E divide in 

 such a manner that we have E\, E2, and E'l, E'2, as is shown 

 from the lower pole in Fig. 14 and from the side in Fig. 15. 

 In Fig. 14 it will be seen that the pigment in Ez and E'2 is 

 massing close to the cells A and A', and this heralds the for- 

 mation of Et^ and E' t, which are shown in Fig. 1 5 from the side 

 and in Fig. 16 from below. In this latter figure it will be 

 noticed that ^3, E' y By and B' ^ form as it were a cross on the 

 lower pole, with the cells A and A' in the center of it. In Fig. 

 17 (the same stage as shown in Fig. 16) the ovum is viewed 

 from the lower pole and drawn as if transparent. The cells 

 Ey E' y E2, E'z, By B' y A and A' lie on the surface and partly 

 conceal Ei, E'l, Bi, B'l, Bz and B'z, which lie below them, 

 while Dr, Dl, D'r, D'l, Cr, CI, Or, C'l are completely hidden 

 and indicated by dotted lines. 



Presently the cells Ei, Ez, E'\, E'z, divide in a plane 

 parallel to the long axis of the ovum so that Eir, Eil, Ezr, 

 E2I, E'lr, E'll, E' 2r, E'zIqxq formed as is shown in Fig. 18. 

 The relative position of these cells is best shown in Fig. 19, in 

 which the ovum is again treated as if transparent. Almost 



