42 PROCEEDINGS OF THE ACADEMY OF [1896. 



microscopical characters has led to a remarkable increase in the 

 number of recognized species. Only the other day, I received a new 

 part of Marshall's Monograph of British Braconida?, in which the 

 following paragraph is sufficiently significant : — 



" Nearly a dozen species [of Asj)ilota] have been indicated or 

 described ; tiieir inconstant characters render precise definition ex- 

 tremely difficult, and tabulation almost impossible. . . . Accident 

 has brought to light some facts relative to one species, nervosa Hal., 

 from which it appears that the varieties mentioned by that author 

 [Haliday] belong almost certainly to several distinct species. The 

 fascicornis Hal., requires to be elucidated in a similar way, for the 

 capture and examination of isolated examples of unknown ori- 

 gin, lead to very uncertain results." (Tr. Ent. Soc. Lond., 1895, 

 p. 375). 



Now in Perdita precisely the same state of afiairs occurs, and it 

 will thus be found that while certain species (e. g., crotonis, luteola) 

 are very easily recognized, some others (e. g., bakerce, verbesmce) are 

 almost as well to be called races or varieties as species. In the 

 opinion of the writer, we have indeed the process of evolution going 

 on under our eyes, the puzzling forms being those which have only 

 lately segregated themselves, and have not yet developed striking 

 peculiarities. 



Take for example bakerce, the closest ally of the Cleome species 

 zebrata. It does not appear to diflTer more from zebrata than the 

 mutations of the latter do from one another, and in the female is 

 practically identical with it so far as outward signs go. But the S 

 bakerce has a slight but constant difference in its wider supraclypeal 

 mark, and it also differs in its genitalia. These differences would 

 never have been noticed, in all probability, had not bakerce been 

 observed to differ in its habits from zebrata, to frequent not the 

 Cleome, but Golden-rod. In fact, the similarity is so great that Mr. 

 Fox, after seeing specimens, expressed the opinion that bakerce was 

 a synonym of zebrata. 



Another case, not less perplexing, is found in the albipennis-ver- 

 besince-lepachiclis series. The males of this series, placed in a row, 

 readily separate into those which have narrow yellow bands on the 

 abdomen and those which have not. Those with the bands separate 

 into a series with the flagellum orange, and one with it blackish, and 

 it is seen that the former are from Verbesina, the latter from Helian- 

 thus. 



