PARTHENOGENESIS 179 



with her proboscis, which causes a proHferation of the 

 cells of the leaf. Eventually the leaf cells grow so fast 

 that the stem mother is overarched in the gall that she 

 has called forth. 



Inside the gall she begins to lay her eggs.. From these 

 eggs emerge young individuals that remain in the gall 

 until they pass their last molt, when they become winged 

 migrants. Externally all the migrants are alike ; but 

 if they are dissected, it will be found that some of them 

 have large eggs, some small eggs. But all the offspring 

 of the same mother are of one or of the other sort. 



The migrants crawl out of the opening in the gall and 

 fly away. Alighting on other hickories, they quickly 

 deposit their eggs. From the large eggs the sexual 

 females emerge. They never grow any bigger than the 

 egg from which they hatched. In fact, they have no 

 means of feeding, and contain only one large egg with 

 a thick coat — an egg almost as large as the female 

 herself. 



From the small eggs of the migrants, minute males 

 are produced — ripe at their birth. They fertilize 

 the sexual female. She then deposits her single egg on 

 the bark of the hickory tree. From this egg (that lies 

 dormant throughout the entire summer and following 

 winter) there emerges next spring a female, the stem 

 mother of a new line. 



Here we find three generations in the cycle — two 

 of which reproduce by parthenogenesis. The first 

 parthenogenetic generation gives rise to two kinds of 

 individuals — one makes large eggs, the other small 

 eggs. The large eggs produce sexual females, the small 

 eggs males. 



