PLATE 3 



EXPLANATION OF FIGURES 



10 Section of capsule showing first polar body at the left of the egg, and the 

 male pronucleus inside. Several degenerating yolk cell nuclei and one degener- 

 ating spermatozoon in the yolk. X 730. 



11 Another section of the same capsule in which the yolk cell membranes 

 have not yet disintegrated. X 730. 



12 Drawing from life of a capsule freed from the mother by pressure, showing 

 natural condition of yolk and mitochondrial mass, one egg and one embryo. 

 X 520. 



13 Two eggs of one capsule showing progressive steps in the cutting off of 

 the first micromere. X 730. 



14 Section through an embryo of about 72 cells. Three germinal regions 

 are indicated, the primary entoderm (4 cells showing) at the left, mes-ectoderm 

 at the right and secondary entoderm lying between. Yolk cell membranes and 

 nuclei have entirely disintegrated. X 730. 



15 Drawing from life of an embryo at the same stage as that in the pre- 

 ceding figure. X 730. 



cap., capsule 



cent., centrosome 



d.sp., degenerating sperm 



d.j/.n., degenerating yolk cell nucleus 



ent.l, primary entoderm 



ent.2, secondary entoderm 



inf., infiltration 



mid, first micromere 



mil., mitochondrial mass 



p.b.l, first polar body 



7/., yolk 



y.c, yolk cell 



cf, male pronucleus 



544 



