178 THE CANADIAN ENTOMOLOGIST 



REMARKS ON THE BASIC PLAN OF THE TERMINAL ABDOMINAL 

 STRUCTURES OF THE MALES OP WINGED INSECTS. 



BY G. C. CRAMPTON, PH. D. 



Massachusetts Agrii:ultural College, Amherst, Mass. 



The genitalia of male Hymenoptera, Neuroptera, Mecoptera, Diptera, 

 Trichoptera, Lepidoptera, Hemiptera (Homoptera) and Strepsiptera have been 

 compared with those of the lower orders in a paper which appeared in "Psyche," 

 (June, 1920). The added knowledge gained from this study of a wider range 

 of forms, and from an examination of the condition occurring in arthropods 

 related to insects, together with the light thrown upon the nature of the parts 

 in the lower insects in Dr. Walker's recent description of the genitalia of the 

 male of GrylloblaUa campodeiformis (Can. Ent., LI, 1911), p. lol) have enabled 

 me to come to a better understanding of the fundamental composition of the 

 terminal structures of the Hexapoda, and the following suggestions are here 

 offered in an effort to clear up some of the uncertainties concerning the inter])reta- 

 tion of the parts in insects in general and in the higher forms in particular. 



Embryologists have maintained that the abdomen of an insect is primarih' 

 composed of twelve segments — or eleven segments, with a "telson" — and since 

 the abdomen of the Protura. (which are among the most primitive representa- 

 tives of the Hexapoda) is composed of twelve segments, there is some evidence 

 for considering that twelve is the original number of segments entering into the 

 composition of the abdominal region of insects in general. It is only in excep- 

 tional cases, however, that traces of the structures interpreted as the A'estiges 

 of a twelfth segment are retained (as in certain odonatan nymphs), and the 

 retention of even eleven complete segments is by no means of common occurrence 

 in the lower pterygotan orders, since the eleventh tergite ("11*" of Fig. 5) is 

 usually lost through atrophy of fusion with the preceding tergites, though 

 certain latero-ventral parts of the eleventh segment are frequently retained to 

 form the so-called paraprocts "e" (Figs. 1 and 5) of lower insects. 



The paraprocts "e" (Figs. 1 and 5) are usually much reduced, and unite 

 with the tergites of the tenth or other segments to form the anal j)apilla or 

 proctiger (a structure bearing the anus) in higher forms (Fig. (i, "h"). The 

 paraprocts, "e", are represented as though distinct, in the diagram of the parts 

 of a sawfly .shown in Fig. 3; but this does not correspond to the actual con- 

 dition occurring in any known sawfly, since llu- paraprocts in these insects 

 usually form the floor (and sides) of the anus-bearing structure whose tergal 

 region is made up largely of the tenth tergite — whjch usualK unites more or 

 less closely with the ninth tergite in the sawfly group. 



The cerci, 'f",' borne on the paraprocts "e" (Figs. 1, 3 and 5) are homologtjus 

 with the multiarticulate flagelliform uropods of such (Vustacea as the Tanaidacea 

 (Chelifera). The exopodite, or outer branch of (he biramous appendage form- 

 ing the uropod, is sometimes wanting in these flagelliform uropods of the Tanai- 

 dacea, thus suggesting that when only one of (he branches is retained, (he 

 endopodite, or inner (jne, remains lo form (he cerci of inseiis. When l)otli 

 branches of the uropod are retained in the Tanaidacea, they are l)()rne upon a 

 single segment or prolopodite (if one may judge from the pifl)lished flgures of 

 these structures, and from tlie condition exhibited by Apseudes spinosus) and 

 on this account I have been led to conclude that Walker, 1919 (Ann. Ent. Soc. 



August, 1920. 



