OF WASHINGTON, VOLUME XVIII, 1916 135 



First taking a prionine larva such a comparison will show that 

 the anterior and posterior cuneal notches gradually separate as 

 they approach the thorax. The former pushes dorsad, the latter 

 ventrad. This produces a lengthening of the muscles s-pn 2 

 between them, together with a gradual reduction in the number of 

 fibers until in the metathorax but two remain. Muscle band 

 s-pn becomes more horizontal and in the first abdominal segment 

 extends entirely across the segment (s-s-pri), to a point on the 

 superior cunae. This muscle is retained in the thoracic segments. 

 The muscle defining the scutal line (sc.-pn) loses many fibers as 

 it approaches the thorax and suddenly disappears in these seg- 

 ments. It is also absent in the abdomen of some other families. 



Now if the integument free of muscles is studied it will be seen 

 that between the cuneal wedges a gradual reduction of the con- 

 necting portion of the intersegmental skin (Is.S) takes place 

 towards the thorax; so that between the metathorax and the 

 first abdominal segment the anterior and posterior notches lie 

 nearly in the same line, and the intervening skin is very short. 

 These wedges and notches actually come into the same plane 

 between the first and second, and second and third thoracic 

 segments. 



This construction necessarily prohibits the telescopic movements 

 of the abdominal segments. The longitudinal muscles between 

 these cunea are gradually collected and narrowed into a dorsal 

 and ventral wedge-shaped band which becomes respectively 

 the superior (s-rt) and inferior retractor (i-rt) muscles of the 

 head. The dorsal are attached to a point at the fusion of the 

 posterior limit of front and the epicranial halves, the ventral 

 at the point of fusion of the collar of prothorax, and the hypostoma. 

 Several other lateral longitudinal muscle bands (c-l) are attached 

 to the collar or skin connection between head and prothornx 

 around the occipital foramen. 



With the widening movement of the cuneal notches the par- 

 ascutal line is gradually lowered but the muscle (pasc-sp) which 

 defines this line gradually, approaching the thorax, moves its 

 attachment dorsally forward until it is attached in the thorax on 

 the anterior notch of the superior cunea (s-sp). In some Cer- 

 :mibycinae larvae this muscle moves posteriorly upward and be- 

 comes attached to the cunea behind [see broken muscles of Cer- 

 ambycinse figure (Plate 8).] In some Asemiinae it is attached 

 along the scutal line and does not reach the cunea. Suddenly 

 in the mesothorax the abdominal muscles from tergopleural 

 suture to postcoxal area and coxal lobe or sternal line (tp-pcx. 

 tp,st) have extended their dorsal attachment to the parascutal 

 (now called scutal line). These muscles are collectively c.-illed 



