THE METAMORPHOSIS OF INSECTS 199 



It has been shown by Gonin ('92), Kellogg ('01 and '04), and 

 Verson ('04) that histoblasts which are the rudiments of the legs of the 

 adult exist within the body-wall of the caterpillar at the base of the 

 larval legs. . Late in the larval life the extremity of the legs of the 

 adult are contained in the legs o f the caterpillar. It has been shown 

 that the cutting off of a leg of a caterpillar at this time results in a 

 mutilation of the terminal part of the leg of the adult. 



The development of the legs of the adult within the body of cater- 

 pillars has not been studied as thoroughly as has been the develop- 

 ment of the wings ; but enough is known to show that in some respects 

 the two are quite similar ; this is especially true of the development of 

 the tracheoles and of the tracheae. 



The development of the legs in insects with vermiform larvae. In 



vermiform larvae the development of the entire leg is retarded. The 

 leg arises as a histoblast, which is within the body and bears, in its 

 more general features, a resemblance to the wing-buds of the same 

 insect. The development of the legs of vermiform larva? has been 

 studied most carefully in the larvae of Diptera. During the larval 

 life the leg becomes quite fully developed within the peripodal cavity; 

 in Corethra, they are spirally coiled ; in Musca, the different segments 

 telescope into each other. At the close of the larval period, the 

 evagination of the legs takes place. 



C. THE DEVELOPMENT OF ANTENNAE 



i. The Transformation of the Antenna of Nymphs and of Naiads 

 In the case of nymphs and of naiads the insect when it emerges 

 from the eggshell has well-developed antennae. The changes that 

 take place during the postembryonic development are, as a rule, com- 

 paratively slight; in most insects, an increase in the number of the 

 segments of the antennae takes place ; but in the Ephemerida, a reduc- 

 tion in number of the antennal segments occurs. 



2. The Development of the Antenna in Insects with a Complete 



Metamorphosis 



One of the marked characteristics of larvae is the reduced condition 

 of the antennae; even in the campodeiform larvae of the Neuroptera, 

 where the legs are comparatively well-developed, the antennae are 

 greatly reduced. 



In cruciform larvae the development of the antennae follows a 

 course quite similar to that of the legs. The larval antennae are small 



