NO. 2 ENCYCLOPEDIA OF INSECT ANATOMY — SNODGRASS 39 



Each primary lobe divides distally into two secondary lobes, a 

 median mesomere, and a lateral paramere. Then in most cases the 

 mesomeres unite by their edges to form a hollow median organ, the 

 aedeagus, with the gonopore in its base; the lateral parameres be- 

 come the claspers of the adult. The genital organs of the Orthoptera 

 begin their development in this way as a pair of lobes that divide, 

 but in their later growth they take on such a diversity of structure 

 in the different families that the adult organs have little or no like- 

 ness to the genitalia of the other orders. 



It is in the Hemiptera that we first encounter the genitalic struc- 

 ture typical of the higher orders. The mesomeres of the primary 

 genital rudiments unite to form the median aedeagus, the parameres 

 become the adult genital claspers. This same genitalic complex, 

 though with many modifications, can be followed through to the most 

 highly evolved orders. The parameres may be simple lobes, as in 

 Hemiptera and Coleoptera, but in the other orders each is usually 

 differentiated into a basal part and a muscularly movable distal part. 



The known development of the genitalia leaves little doubt of the 

 homologies of the major parts in the different orders. A great diver- 

 sity in the genitalic nomenclature from one order to another, how- 

 ever, has grown up because most taxonomists are ordinal specialists 

 and hence are interested in maintaining an established set of descrip- 

 tive names handed down from their predecessors. This contrasts with 

 their proclivity at changing the Latin names of the species and genera 

 with which they deal. But a uniform nomenclature is desirable, as 

 well as now being possible, and the lack of a uniform genital termi- 

 nology is highly inconvenient to the nonspecialist and must be dis- 

 tressing to teachers and their students. 



The common assumption that the primary genital lobes represent 

 a pair of former legs has given the parameres the theoretical status 

 of "gonopods." When divided, the basal part is identified as the 

 "gonocoxite," the distal part as the "gonostylus." The aedeagus is 

 then supposed to have been formed by the union of endite lobes of 

 the "coxites." All this does very well as a basis for a practical no- 

 menclature, but a leg origin of the genitalia has never been demon- 

 strated or even supported by any concrete evidence. The postem- 

 bryonic origin of the primary lobes and their median position behind 

 the sternum of the ninth abdominal segment are in strong contrast 

 to the true limb vestiges seen in the embryonic abdomen. There is 

 no evidence that the mesomeres are endite lobes of the parameres. 

 The primary genital lobes arise on the venter of the ninth abdominal 

 segment, but always behind the region of the sternal plate. The adult 



