ARTHROPODA 289 



changes can only be realized by a comparison of the structure 

 of a caterpillar and of the butterfly into which it develops. The 

 larvae may be suited to aquatic life, the adult to aerial ; the larva 

 may be carnivorous or herbivorous, the adult may live on the 

 nectar of flowers. These changes of habit are closely correlated 

 with the changes of structure noted in the metamorphosis. 

 The reproductive organs are not mature until the imago stage 

 is reached. Frequently the imago only survives long enough 

 to insure the laying of fertilized eggs. In general the length of 



FIG. 130. 



FIG. 130. Violet Land-crab. After Shufeldt. 



Questions on the figure. Compare the crab with the lobster (Fig. 132) as to 

 the development of the body-regions, segmentation, appendages, etc. Compare 

 all the figures of crabs available and note in what respects they vary externally. 



331. Library References. Make a report on the metamorphosis in Crustacea. 

 What is meant by an incomplete metamorphosis? Illustrations. 



life in insects is short, although it is claimed that queen bees 

 may live five years and queen ants thirteen. The Crustacea 

 are much longer lived. 



332. Ecology. When we remember the great number of 

 species and of individuals in the group of arthropods we are 

 forced to realize something of their importance in their rela- 

 tion to other forms of life on the earth. Their numbers and 

 their enormous power of reproduction make it inevitable that 

 they become pests and threaten the existence of the plants and 

 animals on which they prey, and likewise that they become 

 19 



