NO. 6 CATERPILLAR AND BUTTERFLY — SNODGRASS 41 



observed that the imaginal muscle rudiments must first be innervated 

 to begin development. It seems, then, that myoblasts can assemble at 

 the mechanically correct place for a specific new muscle, but here they 

 must wait for a nerve connection before they can form the muscle. 

 Finlayson (1956), in a further discussion of the relation of innerva- 

 tion to muscle development, says that sheets of fine muscle fibers lying 

 under the epidermis of adult moths develop in the absence of innerva- 

 tion. (Possibly he refers to the heart muscles.) 



The fat tissue, or so-called fat body, of older caterpillars still in 

 an active condition consists of flat branched and lobulated cell masses 

 having sharply distinct outlines. In the early pupa the fat masses 

 break up into large granular cells, which later become ragged and 

 frayed, and finally go into a state of disintegration, liberating their 

 granular inclusions and droplets of oily fat. This material becomes 

 food for the developing imaginal tissues, and in the lepidopteron much 

 of it must be carried over to the adult to supplement the meager diet 

 of the moth or butterfly. 



The alimentary canal of the larva (fig. 7), as already shown, is 

 entirely remodeled in the pupa in adaptation to the liquid diet of the 

 adult (fig. 4). Verson (1905) gives a detailed description of the larval 

 alimentary canal of the silkworm Bombyx mori and the metamorphic 

 processes beginning at the time of cocoon spinning. The stomodaeum 

 and proctodaeum are enlarged from circular growth centers, the 

 so-called imaginal rings, at their inner ends. The degenerating larval 

 epithelium of the mesenteron is thrown off into the lumen, and is 

 replaced by an imaginal epithelium formed from groups of persisting 

 regenerative cells. Essentially the same process of mesenteron recon- 

 struction is described by Henson (1929) for Vanessa, and by Blau- 

 stein (1935) for Ephestia kiihniella. The moth of Ephestia takes no 

 food, and the stomodaeum is said by Blaustein to be reduced to a 

 narrow tube closed from the mesenteron by a solid mass of cells. Some 

 other moths that do not eat, such as the tent caterpillar moth, still 

 retain an intact alimentary canal, suggestive that fasting in the adult 

 stage is a recently acquired habit with them. 



The fact that the organs of the pupa, external or internal, are those 

 of the adult in a formative stage, and that the larval organs are cast 

 off with the moult to the pupa, or go into dissolution within the pupa, 

 supports the view that the pupa is a preliminary stage of the adult. 

 For the attachment of the muscles on the adult cuticle, therefore, a 

 secondary moult is necessary. This is the theory of Poyarkoff (1914), 

 which is upheld by Hinton (1948), by Rockstein (1956), and by 

 DuPorte (1958). An opposing theory, that of Jeschikov (1929), 



