40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 143 



go into complete dissolution. Important muscles of the imago having 

 no representatives in the larva are newly formed in the pupa. 



In the Lepidoptera the dorsal and ventral bands of longitudinal 

 larval muscles are preserved at least into the pupa. In the pharate 

 pupa of Malacosoma americanutn these muscles remain clean and 

 intact with distinct striations, and are active through the pupal stage, 

 enabling the pupa to move its abdomen. According to Finlayson 

 (1956) the longitudinal muscles degenerate during the first two days 

 of adult life. On the contrary, the fibers of the outer system of body 

 wall muscles in the larva of Malacosoma are already in the pharate 

 pupa distinctly in a state of disintegration. They have lost their 

 healthy appearance, looking soft and flabby, and their striations are 

 faint or gone. Associated with these muscles are always large numbers 

 of phagocytic cells, and in the mature pupa this system of larval 

 muscles completely disappears. 



The adult musculature of the thorax of Telea Polyphemus has been 

 fully described and illustrated by Nuesch (1953). Both the thorax 

 and its musculature are entirely reconstructed in the pupa. Blaustein 

 (1953) gives a detailed account of the histogenesis of a longitudinal 

 wing muscle in Ephestia kuhniella. Small undifferentiated cells 

 destined to become muscle cells, or myocytes, assemble where the 

 new muscle is to be. By division these myoblasts form a syncytium 

 of muscle cells during the first days after pupation. The cells then 

 unite into long strands that become muscle fibers. The nuclei move 

 to the periphery, a sarcolemma is formed, and fine thickenings in the 

 myoplasm become fibrillae. Development of the muscle is completed 

 by the twelfth day of the pupa, on the thirteenth the striations appear. 

 Finally the completed muscle is attached to the body wall. 



The vision of a muscle being independently formed in the midst 

 of chaos within the pupa is a most mysterious thing in insect metamor- 

 phosis. In the first place, what directs the wandering myoblasts to 

 assemble at the place where a specific muscle must be? Second, what 

 compels the assembled myoblasts to go through the changes and com- 

 plex associations that result in the formation of a contractile muscle? 



The formation of most imaginal muscles, at least in some lepidopter- 

 ous pupae, depends on their connection with nerves. Williams and 

 Schneiderman (1952) and Williams (1958) describe experiments on 

 diapausing pupae of Cecropia and Polyphemus from which the entire 

 nervous system had been removed. When induced to develop, these 

 pupae transformed into externally perfect moths, but on dissection 

 they were found to be completely without muscles, except for the 

 muscles of the alimentary canal and the heart. Others likewise have 



