30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



SUMMARY 



A general plan of muscle arrangement can be recognized in 

 orthopteroid insects, and the same plan is found in representatives 

 of other orders. It is possible to discover apparent homologies among 

 muscles on the basis of origin and insertion, though one or both 

 attachments may vary considerably among the different species. 

 There are certain muscles that evidently are homologous with those 

 of the generalized plan, but which because of some variation or modi- 

 fication in origin or insertion are difficult to identify. On the other 

 hand, some muscles are aberrant and cannot be reconciled with any 

 plan. 



Some unusual muscles and structures, and relationships between 

 muscles and skeletal parts, were encountered in this study. 



The following muscles occurred only in the species of Orthoptera 

 included in this work: the hypo pharyngeal muscle of the mandible, 

 14 (fig. i) ; the anterior dorsal dilator muscle of the salivarium, 15 

 (fig. i) ; the depressor muscle of the labial palpus, 2^ (fig. i) ; the 

 muscles of the labial palpus, 2^, 26, and <?/ (figs, i, 3A) ; and the 

 flexor muscle of the glossa, 28 (figs, i, 3). 



In Periplaneta americana L., Orthoptera, the compressor muscle 

 of the labrum, i (fig. 2), is asymmetrical; the dilator muscle group 

 of the labrum, 2 (fig. 2), and the dorsal dilator muscle of the cibarium, 

 8 (figs. I, I A, 2), were observed only in this species. 



The muscle of the hypopharynx, ip (figs. 5, 6), in Anisolabis 

 tnaritima Gene, Dermaptera, arises centrally in the midregion of the 

 mentum and not on the tentorial bridge as is the usual manner. 



In both the adult and larval forms of Corydalus cornutus L., 

 Neuroptera (figs. 9, 11), the prementum is divided into three sclerites. 

 The muscle group jj (fig. 11) was observed to be especially well 

 developed only in the larva of Corydalus. 



The two muscles J4 and J5 (figs. 14, 15) were observed only in 

 the adult Sphecius speciosus (Dru.), Hymenoptera. The muscle of 

 hypo pharyngeal bar Y, 10, of the generalized plan is absent; this is 

 the only case in which this condition was observed. The dorsal muscle 

 of the labium, 20A (fig. 13), was found only in this species. 



In Harpalus caliginosus F., Carabidae (adult), muscle 21 A (fig. 19) 

 is an additional labial muscle that is not found in the other insects 

 included in this work. It is in this species also that the posttentorial 

 apodeme, PTN (fig. 19), occurs; all of the labial muscles arise on this 

 structure, as does also the muscle of the hypopharynx, ip (fig. 19). A 

 similar apodeme is found in Dineutes discolor Aube., Gyrinidae 



