264 GERM-CELL CYCLE IN ANIMALS 



Reduction 

 Division 



Ripe Eggs 



Polar Body 



Oogoniun () ^ ^ 



Fertilized 



Egg 



Fertilized 

 Egg 



Spermat- 



ogonium 



\^ *** ^/ T;*^: 



Sperm 



FIG. 69. Diagrams showing the behavior of the chromosomes during 

 maturation and fertilization in the starfish, Echinus. One kind of 

 spermatozoon is formed, but the ripe eggs differ, one containing a 

 large X-element, the other a small Y-element. (From Schleip, 1913.) 



X 



Protenor, Anasa Syromastes, Homo Ascaris lumbricoides 



t 



Rocconola, PrionideA, Gelastocoris Acholla 

 JTitchia Sinea multispinosa 



FIG. 70. Diagram showing the number and size relations of the X- and 

 Y-chromosomes in a number of animals. (From Wilson, 1911.) 



