132 HEREDITY AND ENVIRONMENT 



A ^^ B 



Fig. 33. Spermatogenesis or a Nematode Worm {Ancyra- 

 canthus). A, chromosomes of sperm mother cell, 11 in num- 

 ber, before their union into pairs. B, early stage of first 

 division; 10 of the chromosomes have united into 5 pairs and 

 each of these has split lengthwise; 1 chromosome remains un- 



