2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



of a grasshopper. The principal difference between the two is that the 

 wings of the young grasshopper develop externally, and those of the 

 caterpillar grow internally within pockets of the skin beneath the 

 cuticle. Likewise, a "legless" fly maggot has legs developing in 

 pouches of the skin covered by the cuticle. A young grasshopper goes 

 over directly into a mature grasshopper; the caterpillar, the maggot, 

 and others of their kind, when full grown with plenty of food stored 

 in their bodies, must undergo a second transformation in a pupal stage 

 to be restored to the parental form. This is the usual course of 

 metamorphosis among the insects. 



Most of the Crustacea, on the other hand, hatch at an early stage of 

 embryonic development, though at varying periods of immaturity, 

 w-hen they have only a few body segments and corresponding ap- 

 pendages. During their development after hatching they successively 

 add new segments and appendages until the definitive number is 

 attained. The majority of crustaceans are thus anamorphic in their 

 manner of postembryonic growth, though a few are epimorphic. 



Anamorphosis involves a change of form during development, but 

 it is merely a way of growing, common to crustaceans, diplopods, and 

 some chilopods. It should not be confused with changes of form that 

 have nothing to do with progressive development toward the adult; 

 such changes constitute a true metamorphosis. The metamorphoses 

 of Crustacea are changes of form that the growing animal may take 

 on at successive stages of its anamorphic growth, including the sex- 

 ually mature stage of many parasitic species. In such cases, meta- 

 morphosis has been superposed on anamorphosis. As Gurney (1942) 

 has said, "it may be assumed that development in the Crustacea was 

 primitively a continuous process of growth and addition of somites 

 and limbs, as we find it to be in some branchiopods, and that abrupt 

 changes between successive moults leading to the origin of definable 

 phases are secondary responses to changes in the habit of life of the 

 larva and adult." Gurney notes an apparent exception to this rule in 

 the Euphausiacea and some Penaeidae, in which the larva and the 

 adult lead much the same kind of life. The successive phases of de- 

 velopment in these two groups, however, are mainly stages of ana- 

 morphic growth; their only metamorphosis is the adaptation of the 

 larval appendages for swimming. 



Insect larvae may undergo metamorphic changes of form during 

 their growth, but with the insects this larval hcteromorphosis, com- 

 monly called "hypermetamorphosis," affects the fully segmented young 

 insect, and is therefore not comparable to the heteromorphic larval 

 growth of most Crustacea. Some metamorphosed young insects trans- 



