WALTER] CLASPING ORGANS IN HYMENOPTERA 79 



in the pitch of the tone, and it is only this that is essential here. The 

 pitch of the wing-tone in flight is given by Landois (1867, p. 69) for 



Apis A ^jjJ : for Bombus terrestris, small male, 



larger male of the same species fo L J— - ; and for a large female 



of Bombus muscorum. fa I I have determined the w T ing- 



tone of Sirex gigas and Rhyssa pcrsuasoria as J \ ; . In many 



Ichneumonidae, and in all Formicidse no measurable tone of flight 

 can be heard. These great differences in the pitch of the tone of 

 flight of the Anthophilids and Vespidae on the one hand and the Ten- 

 thredinidae, Ichneumonidae, and Formicidse on the other, doubtless 

 confirm the conclusion, forced upon one by a comparison of the struct- 

 ure of their flying organs, that the latter move the wings more slowly 

 than the former. This difference in the rapidity of wing-movement 

 evidently has its cause in the difference of proportion of the wing-area 

 to the weight of the body : the Anthophilidae and Vespidae possess 

 relatively much smaller wings than the Tenthredinidae, Ichneu- 

 monidae, and Formicidse. If the wings of Sirex gigas are compared 

 with those of Vespa crabo, the fore wing alone of the Sirex will be 

 found to cover both wings of the larger and stouter hornet. Rapid 

 and precise flight is probably only possible for those Hymenoptera 

 which have firmly united fore and hind wings. Experiments made 

 to prove this would be of doubtful value, since the removal of the 

 hooks or the groove mutilates the wings to such an extent that it 

 would be impossible to judge what part of the resulting peculiarities 

 of flight should be attributed to the loss of the clasping apparatus 

 and what part to other causes. I have several times observed bum- 

 blebees remarkable for their laborious, aimless, and wavering flight ; 

 a close examination of such always showed the hooks much injured, 

 probably by w r ear. 



VI. Systematic Part 



The idea readily suggests itself to utilize the arrangement, number, 

 and development of the hooks of the hind wing for systematic pur- 

 poses. The first attempt in this direction, which was also the last, 

 was made by Staveley, who ascribed a considerable systematic value 

 to the hooks. Andre, who, however, otherwise does not approach 

 the subject more closely, is very skeptical in this respect (1882, p. 

 65). Staveley has published a key, which, based upon the morphol- 



