NO. 6 



INSECT ABDOMEN SNODGRASS 



43 



to correspond with the external dorsal and ventral ninscles usually 

 more definitely difl'erentiated from the internal muscles in the majority 

 of the Pterygota. 



The true lateral body muscles of llphemerclla include only the 

 intrasegmental, vertical, tergo-sternal muscles (fig. 15 A, //, 2I, j/), 

 and the intersegmental, oblique tergo-sternal muscle (7/). The 

 groups of branchial muscles (binds), inserted in the larva on the 

 bases of the gills, are described and figured l)y Diirken as arising 

 on the lateral parts of the sterna. The areas on which these muscles 



HIT 



Fig. 15. — Examples of abdominal musculature. 



A, musculature of left half of seventh and eighth segments (seen externally) 

 of abdomen of larva of Ephciiicrclla ignita (from Diirken, 1907) ; hmcls. bran- 

 chial muscles, shown here as originating on lateral part of sternum, which is 

 probably the ventral area of limb basis (see fig. 34 B). 



B, muscles of right half of third abdominal segment (seen internally) of an 

 acridid, Dissosfeira Carolina. 16/, internal median dorsals ; 168, internal lateral 

 dorsal ; i6q, paratergal muscle ; i/o, external median dorsal ; ///, external 

 lateral dorsal ; //i", median ventral ; 77.?. internal lateral ventral ; 1/4, external 

 lateral ventral ; 175, 176, internal laterals ; 777. 771^, 779, external laterals ; id, 

 insertion point of dorsal transverse (cardiac) muscles. 



arise, however, are clearly distinct from the true sterna (fig. 34 A, 

 B, Stn), and very evidently represent the bases of the abdominal 

 limbs (LB), of which the gills (Brn) are the distal movable parts. 

 The branchial muscles, therefore, are not body muscles, but are in- 

 trinsic muscles of the appendages, and take their origins within the 

 Hmb bases. The true lateral body muscles (fig. 34 A, /) are tergo- 

 sternal in their attachments and lie mesad of the lobes (LB, LB) 

 supporting the gills. The gill muscles of the ephemerid larva, Diirken 

 says, are retained without change in the adult. They do not appear 



