The comparativ study of the normal muscle pattern of the pupa and the 

 experiments carried out indicate that the sections (a, b and c) of the dorsal 

 band break down in a regular sequence. The first to degenerate is (a), as shown 

 by controls of A. pernyi, A. selene and S. cynthia (Fig. 2), and experiments 

 on A. pernyi (Fig. ЗА and B). Next is (c) and last (b) (Fig. ЗА and B). In the 

 pupa of A. polyphemus section (b) may be the only part of the dorsal band 

 of the 3rd segment that remains (Fig, 1). 



The results described so far have established that degeneration of normally 

 persistent muscles can be induced in both diapausing and non-diapausing 

 saturniids, in the 3rd segment at least. I have previously suggested (Fin- 

 layson, 1956) that there are two gradients influencing the rate of muscle 

 histolysis so that it takes place in two waves, one starting at the anterior end 

 of the body and the other at the jjosterior. In the case of the longitudinal 

 muscles of the abdomen these waves stop in the 3rd and 6th segment. Even 

 in the least susceptible species {S. cynthia) the muscles of the 3rd segment 

 can be made to degenerate by denervation. It seemed likely therefore that the 

 muscles of the 6th segment would be more sensitive to denervation than those 

 of the 4th or 5th segments. Experiments carried out with S. cynthia (Table 1) 

 and A. selene showed that this supposition is true. In A. selene removal of the 

 5th ganghon results in more extreme degeneration in the 6th segment than 

 in the 5th. 



Metamorphosis of stretch receptor muscle 



In the Lepidoptera the abdominal stretch receptors, which consist in part 

 of muscle, are closely associated with the dorsal intersegmental muscles 

 but they persist in segments from which the intersegmentals disappear during 

 pupation and thej^ persist in the old adult after the intersegmental muscles 

 have degenerated (Finlayson, 1956, Finlayson and Lowenstein, 1958). 



The muscle of the stretch receptors of Samia cynthia undergoes histological 

 changes during metamorphosis. In the fuUy-grown larva the muscle is clearly 

 striated (although the striations are much fainter than those of ordinary musc- 

 les). There are tAvo giant nuclei in the centre of the organ and small nuclei 

 distributed along the muscle. In the developing adult the muscle striations 

 disappear, the cytoplasm becomes basophilic, some nuclei degenerate and 

 others divide mitotically. In the adult the striations are again visible and there 

 are many small nuclei arranged in roAvs in the muscle. 



Denervation of the stretch receptor muscle by removal of the appropriate 

 ganglia has no apparent effect on the events described and the resulting adult 

 receptors have clearly striated muscles. Thus it appears that motor innervation 

 is not essential for the metamorphosis of the stretch receptor muscle. This 

 result is comparable to that obtained by Wigglesworth (1956) in his study 



102 



