HO ZOOLOGY. 



tain the eggs in special portions of the body until development 

 has well begun. The flies lay their eggs in the decaying matter 

 which the young use as food. The solitary wasps seal theirs 

 up in nests with the food (dead or wounded spiders or insects) 

 on which they are to develop. Other insects bore into the 

 tissues of living plants and deposit their eggs, about which 

 " galls " or masses of abnormal vegetable tissue are developed. 

 The ichneumon fly deposits its eggs in the body of some other 



FIG. 53- 



FIG. 53. Galls on hackberry leaf, produced by a fly (Cecidomyiidce). Natural size. 



Photo by Folsom. 



Questions on figures 51, 52, 53. What does the gall represent from 

 the point of view of the plant? From the point of view of the insect? 

 What seems to cause the undue vegetable growth? Find other galls in 

 nature and try to find what type of insect is responsible for them? In 

 what ways may one hope to determine this fact? 



animal. Thus we see an immense number of adaptations 

 useful to the organism have been developed in connection with 

 the egg-laying habit. After such provision the majority of 

 animals leave the young to care for themselves; but many 

 higher forms take further pains to protect and train their 

 offspring during the course of their development. The care 

 which the birds and mammals give their young is a matter 

 of common observation. It takes the form of food, of special 

 homes, as nests, burrows, dens, etc., and of the personal ser- 



