2/O E. GABRITSCHEVSKY. 



pollen and decayed or injured Bombus larvae (fresh larvae are 

 never attacked). 



The "Mimicry' of Volucella offers a fascinating field for 

 research and one of the steps which must be taken in the pre- 

 liminary study of this case is to find out how close a resemblance 

 there is between a variety of Volucella and the various species of 

 Bombus in the same geographical area. Such a resemblance has 

 been described in my previous paper for the European group of 

 Volucella. I was interested therefore to see if this was true for the 

 American varieties of Volucella. 



Before dealing with this question I wish to refer to some new 

 details on the coloration of the European Volucella Bombylans 

 which must be also taken into consideration in the study of the 

 North American group. Many flies of these species have been 

 collected recently in the central parts of Russia, to see if there are 

 any other variations than those which have been generally 

 described. Specimens of V. Bombylans have been found with an 

 entirely rufous abdomen (PI. I., 2, 9 ), which corresponds exactly 

 to the color of the abdomen of the northern B. laponicus and other 

 allied species. This variety has been collected in Russia only 

 twice in a region where the B. laponicus does not occur. Another 

 variety of V. Bombylans, which may be named V. Bombylans var. 

 flava, is not uncommon. This fly has a spot of yellow hairs on the 

 thorax (PI. I., Fig. 3, 9 ), but the rest of the fly is typical Bomby- 

 lans. (Only females of this type have been collected.) The 

 yellow spot of hairs of this black variety is located in the same 

 place as the black spot of yellow varieties of male V. hasmoroidalis 

 and male V. plumata. It is significant from a genetic point of 

 view that in the European Volucella group of flies only this little 

 area of thoracic hairs is limited to one sex, whereas the entire body 

 coloration is otherwise alike in both sexes. Thus the yellow spot 

 of the black variety seems to appear only in the females, the black 

 spot of the yellow varieties on the contrary is limited to the males 

 (V. plumata and V. hxmoroidalis] . It is, however, possible to 

 find in some localities also females of V. plumata and V. hxmo- 

 roidalis which have a very reduced black thoracic spot of hairs. 

 The black spot itself has often a brown color in the females, but 

 never in the males. The V. altaica from Asia is extremely 



