ITS 



BEREDITY AND SEX 



cycle finds its explanation in these relations except that 

 iln> origin of the two kinds of parthenogenetic females 

 is unexplained. If we were justified in assuming that 

 two classes of female-producing sperm are made in the 

 male, even this point would be cleared up, for in this 



'/ 



I 



lliqiant. )/"< 'f/in-i t 



I 





Fig. 92. — Life cycle of Phylloxera carycecaulis. 



way the two classes of parthenogenetic females could 

 be explained. 



In another group of insects, the aphids and phyllox- 

 erans, the situation is different. 



In the phylloxerans of the hickories there emerges 

 in the spring, from a fertilized egg, a female known as 

 the stem mother (Fig. 92). She pierces a young leaf 



