264 GERM-CELL CYCLE IN ANIMALS 



Oogonium 



Spermat- 

 ogonium 



Reduction 

 Division 



Ripe Eggs 

 (^^ Polar Body 



Fertilized- 

 Egg 



Fertilized 



Egg 



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 



Frotenor, Anasa Syromastes, Homo Ascaris lumlricoides 



YJL 

 X *• 



Nazara 

 viridula 









V 



Euschistus 

 coenus 



6 



iSt 



Nazara 

 hilaris 







Thyanta 

 calceata 



i a 



Rocconota, 

 Fitchia 



Prionides, 

 Sinea 



Gelastocoris 



Acholla 



multispinosa 



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

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



