EXPLANATION OF FIGURES ON PLATES. 167 



PLATE I. 

 All the Figures are drawn from the living object. 



Fig. 1. An embr3 r o (from about the stage of Figs. 29, 30) 

 inside the yolk membrane, which is separated from it in order 

 to show the relative size of the latter. Em., Embryo; dm., 

 vitelline membrane. 



Fig. 2. Egg with polar body (R.) before the fertilisation, 

 vitelline from the surface. 



Fig. 3. Egg shortly before the division into two segmenta- 

 tion spheres. There is still a bridge between the two parts, 

 though it is deficient in yolk granules. The polar bod}- (R.) 

 adheres to the one half. Lateral view. 



Fig. 4. Two-celled stage. The two cells have, since the 

 division, come again into somewhat closer contact. A lateral 

 view. 



Fig. 5. Transition to the four-celled stage, as seen from the 

 pole. 



Fig. 6. Four-celled stage, after the cells have come again 

 into closer contact, as seen from the pole. 



Fig. 7. The same stage on a lateral view (from one corner). 

 A somewhat smaller individual. 



Fig. 8. Eight-celled stage examined in the same way as the 

 former figure. 



Fig. 9. Sixteen-celled stage (a small individual), from the 

 side, but somewhat inclined, so that the eight upper cells can 

 be seen. 



Fig. 10. Thirty-two-celled stage. Lateral view (a large 

 individual). 



Fig. 11. The same in optical section. 



Fig. 12. Further stage, with four upper sixteen-celled tiers 

 and one lower eight- celled. Lateral view. 



