46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



primarily longitudinal and of segmental length, and that they had 

 this arrangement in pre-orthopteroid insects. The internal dorsals and 

 ventrals are likewise often oblique. Obliquity, therefore, would ap- 

 pear to be secondary also in the external muscles, in which it may 

 be so accentuated that the muscles lie in a transverse direction, or are 

 even reversed in position. 



The lateral muscles of the Orthoptera are variable in their positions 

 and in their attachments. They include typical vertical and oblique 

 intrasegmental tergo-sternal muscles, oblique intersegmental tergo- 

 sternal muscles, and in some cases muscles that may be termed " tergo- 

 pleural " and " sterno-pleural," since they are inserted on the lateral 

 membranes or on sclerites below the line of the spiracles. The so- 

 called pleural areas on which these last named muscles are attached, 

 however, probably really belong either to the dorsum or to the venter 

 of the segment, and, if so, none of the lateral muscles is properly a 

 " pleural " muscle. 



In the Acrididae the internal dorsal muscles are distinctly separated 

 into median and lateral groups of fibers (figs. 15 B, 16, i6j, 168) 

 by the points of attachment of the dorsal transverse fibers on the 

 tergum (fig. 15 B, td). The external dorsals assume very oblique 

 or transverse positions (/70, ///). The ventral muscles are well 

 difl^erentiated into median and lateral groups of internal fibers (//i", 

 z/j) and into lateral external muscles {174). The external ventrals 

 {174) are sternal protractors by a complete reversal in the relation 

 between their points of attachment. The lateral muscles in the third 

 and succeeding segments (figs. 15 B, 16) comprise two internal dor- 

 soventral laterals (fig. 15 B, 775, 176), and three external laterals 

 {177, 178, 179). of which the first (//""/") is an abdominal dilator by 

 reason of its sternal attachment being on the upper end of a large 

 lateral sternal apodcme (lAp). The upper ends of the internal 

 laterals {175, 176) are attached on the tergum between the lateral 

 internal dorsals {168) and a broad paratergal dorsal muscle (/6p). 

 This last muscle is the " epipleural " muscle of Ford (1923), who 

 says a similar muscle also is present in the Plecoptera. 



Coleoptera. — The abdominal musculature of adult Coleoptera is 

 known principally from the description of M elolontha vulgaris by 

 Straus-Diirckheim (1828), and of Dytisnis inarf/iiialis by Bauer 

 (1910) and Korschelt (1924). 



The adult musculature of the abdomen of Dytiscus is relatively sim- 

 ple. As described by Bauer (1910) it consists of dorsal longitudinal 

 muscles, ventral longitudinal muscles, and lateral muscles, to which 

 list should be added the transverse muscles of the dorsal diaphragm. 



