NYMPHS, NAIADS, AND LARViE. 



By J. H. CoMSTOCK. 



" Yoti nymphs, called naiads, of the wand'ring brooks." 



— Shakespeare. 



The object of this note is to propose an addition to the 

 terminology of the metamorphoses of insects, which I beheve 

 will tend to make more clear certain fundamental distinctions 

 now generally recognized. 



The older entomologists recognized two types of postembry- 

 onic development of insects. These types were distinguished by 

 various terms, but were most commonly described as incomplete 

 metamorphosis and complete metamorphosis. The term larva was 

 applied by these writers to the early stages of all insects, those 

 undergoing an incomplete metamorphosis as well as those in 

 which the metamorphosis is complete. 



At a later period, during the last quarter of the last century, 

 it was found desirable to distinguish the early stages of insects 

 with a complete metamorphosis from those of insects with an 

 incomplete metamorphosis ; hence the term larva was restricted 

 to the young of insects with a complete metamorphosis and 

 the term nymph, which had been formerly used as a synonym 

 of pupa, was applied to the young of insects with an incomplete 

 metamorphosis. 



In the earlier descriptions of these two types of meta- 

 morphosis account was taken only of the difference in degree of 

 the change in the form of the body that distinguishes the two 

 types; in one the change is partial or incomplete, in the other 

 it is complete. The fundamental reason for this difference was 

 not generally appreciated although it was understood by some 

 writers. 



Fritz MuUer in his "Fiir Darwin" (1864) points out clearly 

 the essential difference between incomplete metamorphosis and 

 complete metamorphosis and in discussing the latter makes 

 the aphorism, "There were, I believe, perfect insects before 

 larvae and pupae." The significance of this aphorism should be 

 clearly understood by every student of entomology, which is 

 far from being the case. This is shown by the fact that fre- 

 quently writers refer to larval characteristics as being more 

 generalized than the corresponding characteristics of the adult. 



