278 BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



streugtbeuing: of the hind legs may be ein])!oycd in the seizing- and 

 retention of the female, but why have tliese acquired peculiarities not 

 had a greater result upon the species ? 



Another question, important to all systematic entomologists, arises 

 from their discussion. Are secondary sexual characters serviceable as 

 generic characters? Contrary to the opinion of many students, I hold 

 that they are. It may strike one as absurd that the sexes may be lo- 

 cated under different genera, but we must bear in mind that a species 

 is comi)osed of both sexes, and it is by the totality of characters that a 

 genus is bounded. But such characters can not be indiscriminately 

 used. Single differences of any kind are suspicious when not accom- 

 panied by others, and sexual characters shonld be avoided as far as 

 possible when both sexes cannot be defined. Among the DoIkhopoflUkey 

 so yich in male characters, species as zoological entities rest chiefly iu 

 the male; the female is a reproducing organ, like the spermiferous 

 barnacle. Classiftcation is made no more difticult by the use of such 

 characters, and is sometimes much simplified; besides it may bring 

 related forms together; and is not this the real end of scientific classi- 

 fication ? 



GEOGRAPHICAL DISTRIBUTION. 



In their geographical distribution, at least so far as the oSTorth Amer- 

 ican fauna is coucirned, the Siirphidce present no remarkable facts^ 

 though not a few of interest. The most noteworthy one is the wide 

 distribution, in general, of genera and species. We have very few pe- 

 culiar genera, and fewer still are aberrant from well-known tyjjes^ 

 Nausigaster being, ])erhaps, the most worthy of note in this respect. 

 Forty-two genera are common to Europe and North America, and 

 nearly thirty of our species are known to be (common to the two con- 

 tinents, and it is very probable that this number will be increased by 

 not a few. Nausigaster is so far known only from North America, but 

 it will undoubtedly be found to occur in South America. Mesograpta 

 is a peculiarly American genus ; indeed, it may properly be called the 

 characteristic genus of our fauna, not only on account of its restriction 

 to this continent, but by reason of the large number of species and the 

 multitude of individuals. Mr. Bigot, it is true, has described s])ecies 

 of Mesograpta from New Caledonia, but it may most safely be said that 

 his determinations are wrong. Asarldna, from Africa, is its nearest 

 extra-American representative. Copestylum, though not differing very 

 markedly from Volucella, may also be considered an American tyi)e. 

 Pterallastes, Teuchoenemis, and Triodonta, though so far known to in- 

 clude only North American species, are feebly characterized, and can 

 hardly be taken into account as distinctive American types. Nor ii* 

 Crioprora a much better example, some of tlie European Brachi/palpi 

 approaching it closely. Eupeodes, Merapioidus, and Senogaster, on the 

 other hand, are wt-ll differentiated American Ibrnis. 



A comparison of the Euroi)ean and North American genera will be 

 of interest, though in general oidy (•oiitiriiiing certain laws of distribu- 



