DIFFERENTIATION OF INDIVIDUALS AND ADAPTATION 117 



her 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- 

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



FIG. 55- 



FIG. 55- Galls on hackberry leaf, produced by a fly (Cecidomyiida). 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? 



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

 some insects, especially the social forms, such as bees, ants, and 

 the like. The lobster carries its young on its abdominal ap- 

 pendages for months after hatching. The lower invertebrates 

 are practically destitute of these later care-taking instincts. 



It is interesting to notice that animals differ very much in 

 their helplessness at hatching or at birth. The young of the 

 reptiles, or the duck, or the chicken are relatively well developed 

 at hatching, and are very soon able to run about and feed (pre- 



