NO. 6 



INSECT ABDOMEN — SNODGRASS 



105 



if true, in establishing an identity between the terminal appendages 

 of larval insects and the appendicular processes of the tenth segment 

 in certain adult holometabolous insects. 



Coleoptcra. — In many families of the Coleoptera the abdomen of 

 the larva is provided with a pair of appendicular processes arising 

 from the dorsum of the ninth segment. These structures have been 

 variously termed styli, cerci, pseudocerci, corniculi, and urogomphi. 



The abdomen of the larva of Dytisciis ends with a transverse pos- 

 terior surface of the narrow eighth segment (fig. 44 A), in the upper 

 part of which the last pair of spiracles open through a median, vertical 

 slit (VII IS p). From the mem])rane below the spiracular area of the 

 eighth segment there arise laterally two slender, tapering processes 

 (ngf) fringed with long hairs. Between the bases of these organs 



VIII 



Fig. 44. — Terminal appendages of coleopterous larvae. 



A, posterior end of abdomen of Dytisciis circumcinctiis larva. B, end of ab- 

 domen of a silphid larva, Thaiiafophilus sp., with exserted anal lobes (from 

 Kemner, 1918). C, end of abdomen of carabid larva, Oodes helopioides, with 

 exserted anal lobes (from Kemner, 1918). 



An, anus ; anl, anal lobes ; ng, urogomph. 



is a small, median plate (IXTf), which appears to be a remnant of 

 the ninth abdominal tergum. Ventral to it is the anal opening (An). 

 According to Speyer (1922, Korschelt, 1924), each of the terminal 

 appendages of the larva of Dytiscus marginalis is provided with three 

 muscles, two inserted dorsally on its base, and one ventrally, all of 

 which arise on the tergum of the eighth segment. 



The morphology of the larval appendages of Dytiscus is difficult 

 to determine. The apparent position of the organs on the rudimentary 

 ninth segment makes it doubtful that they are true cerci, and the dorsal 

 origins of their muscles is not in accord with the musculature of 

 styli. It is claimed by Blunck (1918, Korschelt, 1924) that in all 

 Coleoptera the first two primitive somites of the abdomen are united 

 in the first definitive segment, and that, therefore, the segment bear- 

 ing the terminal appendages is really the tenth. In this case we might 



