50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



the internal laterals of the abdomen occur between the prothorax 

 and mesothorax, between the mesothorax and nietathorax, and be- 

 tween the metathorax and first abdominal segment. They are attached 

 above more nearly on the anterior margins of the terga, and are in- 

 serted ventrally on the intersegmental " furcillae " and on the sternal 

 apophyses. The posterior migration of the upper ends of the internal 

 laterals in the metathorax and abdomen cuts off a lateral group of 

 fibers (/>) from the longitudinal dorsals that evidently corresponds 

 with the paratergal muscle of Dissosteira (fig. 15 B, i6q). 



It is clear that the abdominal musculature of the Dytiscus larva 

 differs in no essential respect from that characteristic of adult insects 

 generally. It presents a more primitive condition in that the internal 

 lateral muscles retain ventrally their intersegmental attachments, 

 whereas in most adult insects, when present, their ventral ends have 

 migrated posteriorly along the edges of the sterna (fig. 15 B, 775, 

 176, fig. 16). 



The figure given by Berlese (1909) of the muscles in the first three 

 abdominal segments of the larva of Pcntodon, and the studies of 

 Boving (1914) and of Craighead (1916) on the abdominal muscula- 

 ture of coleopterous larvae, including species of Cleridae, Trogositidae. 

 Elateridae, and Scarabaeidae, suggest that the chief deviation from the 

 Dytiscus larval muscle pattern consists only of a greater diversification 

 in the position of the muscles, and of an increase in the number of 

 muscles or individual fibers in each group. In any case it is clear that 

 the lar^'al musculature in the Coleoptera presents at most but a small 

 increase in complexity beyond the minimum characteristic of adult 

 pterygote insects. Proceeding from this condition found in the 

 Coleoptera, therefore, we may expect to find that the more complex 

 musculature of other holometabolous larvae represents only a more 

 highly specialized condition. 



Hymenoptcra. — In the larvae of Hymenoptera the body muscula- 

 ture also retains a relative simplicity. The pattern of the abdominal 

 muscles of the h(>nevl)ee larva (fig. 19), as descril)ed by Xelson 

 (1924), departs but little from the basic plan of the general adult 

 pterygote musculature, though it is somewhat more complex than the 

 abdominal musculature of the adult honeybee (fig. 17), and is not at all 

 like the latter in detail. The dorsal muscles of a typical abdommal 

 segment of the larva (fig. 19) consist of broad bands of internal 

 longitudinal fibers {di) of segmental length, and of shorter, oblique 

 external fibers {de). Some of the external fibers, by a transposition 

 of their posterior attachments on the intersegmental fold, have come 



