264 GERM-CELL CYCLE IN ANIMALS 



Odgonium 



Spermat- 

 ogonium 



Reduction R ipe Eggs 

 Division tzs^*- p/,7 Body 



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 ^ H 



Protenor, Anasa Syromastes, Homo Ascaris lumbricoides 



Nazara 

 viridula 



Y 



Euschistus 

 coenus 



JL 



Nazara 

 hilaris 



Thyanta 

 calceata 



t * t 



Rocconoia, PrionideB, Gelastocoris Acholla 

 Fitchia Sinea 



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

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



