DIFFERENTIATION OF INDIVIDUALS AND ADAPTATION 



119 



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 animal. Thus we see an immense num- 

 ber of adaptations useful to the organism have been developed 



Pig. 55- 



Fig. 55. Galis on hackberry leaf, produced by a fly (Cecidomyiidfz) . Natural size. 

 Photo by Folsom. 



Questions on figures 53, 54, 55. — 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? 



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 serv- 

 ices of the parents, who will often protect the young from their 

 enemies at the risk of their own life. Similar care is shown by 



