322 OWEN'S POSITION IN 



which these animals produce with such wonderful 

 fertility in summer, are all fatherless. So are the 

 drones in a hive of bees. 



Among the aphides, this state of things, as a 

 rule, persists throughout the summer ; and it is 

 not until the autumn arrives, that the broods 

 produced take on the characters of males and 

 females, which die after their functions are per- 

 formed and the eggs are laid. The eggs remain 

 dormant during the winter ; and when they hatch, 

 in spring, the aphides produced are sexless, 

 though in some respects they resemble the true 

 females. These sexless forms produce living 

 broods, having the same characters as their pro- 

 ducer ; and these give rise to others, in like manner, 

 through the summer. It has been proved that this 

 state of things may be maintained for three years, 

 by keeping the insects warm and supplied with 

 food ; indeed, there is no positive evidence that it 

 need ever come to an end. 



The males and females are, in many respects, 

 different from the sexless proliferators. Thus, 

 to superficial observation, it appears as if the 

 sexed ' generation,' which may be called the form 

 A, was succeeded by a certain number of sexless 

 4 generations ' of the form B ; these by A, these 

 by B again, and so on. In other words, the * gene- 

 rations ' A and B alternate. 



In the course of the early decades of the nine- 

 teenth century, the wide extension of exact investi- 



