152 



Heredity and Environment 



p 



FIG. 51. SPERMATOGENESIS OF A NEMATODE WORM (Ancyr acanthus). 

 A, Chromosomes of sperm mother cell, n in number, before their union 

 into pairs. B, early stage of first maturation division; 10 of the chromo- 

 somes have united into 5 pairs and each of these has split lengthwise; I 

 chromosome remains unpaired. C, First maturation division after the 5 

 pairs of chromosomes have pulled apart; the unpaired chromosome is 

 going entire to one pole of the spindle. D, Two cells resulting from this 

 division, one containing 5 and the other 6 chromosomes. E, Four cells re- 

 sulting from the division of the two cells like D, in which every chromo- 

 some has split into two so that two of the cells contain 5 and two contain 6 

 chromosomes. F, two of these cells changing into spermatozoa, one con- 

 taining 5 and the other 6 chromosomes. (After Mulsow.) 



