THE EVOLUTION OF INSTINCT 127 



has been emphasized by Weismann and others, but, as 

 Spencer has ably shown, the case is not so easily disposed of. 

 According to Spencer the fact that certain structures and 

 instincts occur hi the workers which are not found in the 

 fertile insects is not because the workers have acquired them 

 since their separation as a distinct caste, but because the 

 fertile insects have lost them. The worker caste is produced 

 by lack of sufficient nutrition. There is a stunting of growth, 

 a failure on the part of the reproductive organs to develop, 

 and in ants an atrophy of the wings and wing muscles. In 

 the early stages of the evolution of the social state the fertile 

 female possessed all the instincts for making the nest, 

 gathering food and caring for the young, as is now done in the 

 more primitive social communities of bees and wasps. In so- 

 cial wasps, as a rule, the occupants of cells richly supplied with 

 food emerge as fully developed females; where the food supply 

 is limited the females are smaller and sterile, and with varied 

 amounts of food various intermediate gradations of size are 

 produced from the largest females to the smallest workers. The 

 smaller individuals which on account of the partial atrophy 

 of their reproductive systems take little or no part in repro- 

 duction busy themselves with building cells and storing them 

 with food, and in taking care of the young. The fertile 

 females live with the rest of the community and share its 

 labors, but in the following year they scatter and form the 

 nuclei of new colonies. At first the queen starts the nest, 

 rears and cares for the young, and performs all the tasks in- 

 cidental to her small household economy. When the young 

 emerge they cooperate in the work of the queen. As the 

 community grows the queen gradually withdraws herself 

 from the labors shared by the workers and devotes herself 

 more and more to laying eggs. 

 Among bees there are numerous gradations between the 



