ARTHROPODA. 



the chitinous covering is usually necessary; these may be ac- 

 companied or preceded by periods of rest, in which important 

 internal changes take place. The metamorphosis is more com- 

 mon among insects (Figs. 140 and 146), although a similar 



FIG. 127. 



FIG. 127. Megalops of Cancer irroratus. From Verrill. x 15. 



Questions on the figure. Compare with Figs. 126 and 129, and make 

 note of the chief points of contrast. Compare also with adult crab (Fig. 

 128). What differences are to be noted between the development in the 

 lobster and in crabs? Is the larval or adult crab more like the lobster? 



thing happens in many of the Crustacea (as crabs, Figs. 126 

 to 128). In spiders the development is direct. The eggs of 

 many insects hatch as worm-like larvae (grubs, maggots, 

 caterpillars). These are usually active, voracious, fat-storing 

 animals, which after a period pass into a resting condition, 

 often surrounding themselves with protective coverings 

 (cocoons). During this quiescent stage they are described as 

 pupa. In the pupal stage the accumulated fat is used by the 

 organism in forming the new organs of the adult or imago. 

 The internal larval organs may be torn down completely by 



