ARTHEOPODA 



289 



the change from larva to adult a series of moultings of the 

 chitinous covering is usually necessary; these may be accom- 

 panied or preceded by periods of rest, in which important in- 

 ternal changes take place. The metamorphosis is more common 

 among insects (Figs. 142 and 148), although a similar thing 

 happens in many of the Crustacea (as crabs, Figs. 128-130). 

 In spiders the development is direct. The eggs of many insects 

 hatch as worm-like larvs (grubs, maggots, caterpillars). These 

 are usually active, voracious, fat-storing animals, which after 



Pig. 129. 



Pig. I2p. Megalops of Cancer irroratus. From Verrill. X IS. 



■ Questions on the figure. — Compare with Pigs. 128 and 131, and make note of 

 the chief points of contrast. Compare also with adult crab (Pig. 130). 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? 



a period pass into a resting condition, often surrounding them- 

 selves with protective coverings (cocoons) . During this quiescent 

 stage they are described as pupcB. In the pupal stage the accu- 

 mulated fat is used by the organism in connection with the 

 formation of the new organs of the adult or imago. Many of 

 the internal larval organs may be torn down completely by the 

 aid of amoeboid cells and be made to contribute material to 

 19 



