44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



to have representatives in the pregenital segments of any other adult 

 pterygote insect. 



Odoiiafo.— The muscles of the first three abdominal segments of 

 adult Odonata are described by Backhoff (1910) and by Schmidt 

 (191 5) in connection with a study of the male genital organs, and 

 some of the abdominal muscles of odonate larvae are figured by Cal- 

 vert (1911,1915). A more complete description of the larval muscu- 

 lature as a part of the respiratory mechanism is given by Wallengren 

 (1914), and of that of the adult by Steiner (1929), while a full 

 account of both the adult and larval muscles in Zygoptera and Anisop- 

 tera will be found in the paper by Whedon (1919) on the morphology 

 of the odonate abdomen, a few errors in which are corrected by 

 Steiner (1929). 



In the abdominal musculature of the Odonata there is nothing 

 to suggest a type of structure more primitive than that of other 

 Pterygota ; the fundamental plan of the muscle arrangement is that of 

 pterygote insects in general, and has little to distinguish it from the 

 muscle pattern of orthopteroid insects. The generalized plan of 

 musculature is best retained in the larvae of Zygoptera. The muscles 

 here comprise internal and external longitudinal dorsals, internal and 

 external longitudinal ventrals, and dorsoventral and oblique lateral 

 muscles. The internal dorsal and ventral fibers are of segmental 

 length ; but the externals in each set are short, taking their origins 

 on the posterior parts of the segments. In the Anisoptera the larval 

 muscles are more strongly developed than in the Zygoptera, evidently 

 as an accommodation to the respiratory and locomotor functions 

 of the rectum, and the broad internal dorsal and ventral bands of 

 fibers take on oblique direction. The adult musculature is much re- 

 duced in the abdomen, and most of the muscles are very short, but 

 the arrangement of the muscles shows no radical departure from 

 the fundamental pterygote pattern better preserved in the larva. 



Orthoptera.— The comparative myology of the abdomen is better 

 known in the Orthoptera than in any other of the larger orders of 

 insects owing to the comprehensive review by Ford (1923) of the 

 abdominal musculature of orthopteroid insects. Then, too, Voss 

 ( 1905) in his thorough study of the thorax of Gryllus includes an 

 account of the muscles of the anterior abdominal segments, and 

 Du Porte (1920) describes the entire musculature of the abdomen 

 in the same genus. 



The abdominal musculature of the Orthoptera and related orders 

 shows in all groups a ditTerentiation of the dorsal and ventral muscles 



