48 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL 85 



of the following sternum. The lateral muscles comprise three tergo- 

 sternal muscles in each side of the segment. .The first (//) is a dilator 

 of the abdomen, since it arises ventrally on the lateral part of the ter- 

 gum and is inserted dorsally on the tip of the lateral apodeme of 

 the sternum; the second and third laterals {2I, j/) are oblique tergo- 

 sternal compressors of the abdomen. 



Fig. 17. — Musculature of two consecutive abdominal segments of adult Apis 

 mclliiica, showing the muscles on the left side. 



Ac, antecosta; del, lateral external dorsal muscle; dil, lateral internal dorsal; 

 dim, median internal dorsal ; il, 2I, jl, first, second, and third laterals ; dls, 

 dilator muscle of spiracle ; Sp, spiracle ; vel, lateral external ventral muscle ; 

 vil, lateral internal ventral ; vim, median internal ventrals. 



The first lateral muscles (//) are dilators of the abdomen, the second and 

 third laterals (2l. 3I) are compressors ; the internal dorsal and ventral muscles 

 {dim, dil, vim. vil) are retractors of the segments, the external dorsals and ven- 

 trals (del, vcl) are protractors. 



THE ABDOMINAL MUSCULATURE OF ENDOPTERYGOTE LARVAE 



The body musculature of endopterygote, or holometabolous, larvae, 

 in its'higher forms of development, attains an extreme degree of com- 

 plexity ; in its simpler forms it differs but little from the body muscu- 

 lature typical of all adult Pterygota. It appears, therefore, that the 

 complex types of larval musculature represent specialized conditions 

 adapting the larvae to their individual ways of living, and are not to 

 be interpreted as meaning that insects are derived from ancestral 

 worm-like forms having an intricate body musculature. The changes 

 in the musculature that occur during the pupal metamorphosis are to 

 be regarded as alterations necessitated by the restoration of the 

 normal adult musculature, which involve varying degrees of destruc- 

 tion or reconstruction in the special, temporary larval musculature. 



Coleoptera. — The larval musculature of Trichoptera and Neurop- 

 tcra has not been fully studied, nor do we have any comparative work 



