52 



BIOLOGICAL LECTURES. 



The next stage was a normal division of I (Fig. 17), and 

 then II, divided (Fig. 18), the cleavage plane, as a rule, lying 



Fig. 17. 



Fig. 18. 



in the extra-ovate. In this way the extra-ovate obtained its 

 nucleus, receiving in this case but one-fourth of the whole. 

 It very often happens that the extra-ovate receives its nucleus 

 later, obtaining in that case a still smaller fragment, but, never- 

 theless, the outcome is a perfectly normal embryo. Later on 



Fig. 19. 



Fig. 20. 



the division takes its regular course. Fig. 19 shows the morula 

 stage, and one recognizes already the double monster. Figs. 

 20, 21 and 22 show double, triple and quadruple gastrulae. 



Fig. 21. 



Fig 



