THB 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 of 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 tracheas. 



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 larvae has been 

 studied most carefully in the larvse 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 ANTENNA 



I. The Transformation of the Antennaz of Nymphs and of Naiads 

 In the case of n3Tiiphs and of naiads the insect when it emerges 

 from the eggshell has well-developed antennee. 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 antennse takes place ; but in the Ephemerida, a reduc- 

 tion in number of the antennal segments occurs. 



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

 Metamorphosis 



One of the marked characteristics of larvae is the reduced condition 

 of the antennse; even in the campodeiform larvas of the Neuroptera, 

 where the legs are comparatively w^ell-developed, the antennae are 

 greatly reduced. 



In cruciform larvae the development of the antennas follows a 

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



