232 AMERICAN HYMENOPTERA. 



a comb of stout spines on the inner side on the apical border 

 (fig. 12). This comb is absent in the males and in Psithyrus 

 (fig. 48). In Bomhis, it guards the pincer-like cleft between 

 the tibia and metatarsus described below, and so forms a 

 part of the structure called the "wax shears" or "pollen 

 mill." 



The hind metatarsi of the females of Bombus are always 

 very broad. This is also true in some species of Psithyrus. 

 In the males of both genera, they are comparatively narrow. 

 In both genera and both sexes, this segment is covered on 

 the inner side with a brush of thickly set, slender and api- 

 cally directed spines. By means of this brush and a similar 

 one, present in both sexes on the inner side of the metatarsus 

 of the middle leg, the bees gather the pollen from their 

 bodies, since they often become covered with this dust from 

 the flowers they visit. When Bombus queens or workers 

 have gathered enough pollen on these brushes, it is scraped 

 off from each over the edge of the tibia of the opposite hind 

 leg and is thus stored in the corbiculae. In this way a large 

 ball of pollen accumulates in each pollen basket. It is prob- 

 able that the males of Bombus and both sexes of Psithyrus 

 use these brushes to clean their bodies and then clean the 

 brushes themselves by rubbing them together. On the poste- 

 rior side of the base of the hind metatarsus of the queens 

 and workers of Bombus there is a prominent and pointed ex- 

 tension. This extension fits against the somewhat excavated 

 apex of the tibia and forms with it a sort of pincer-like cleft. 

 The function of this structure is not certainly known. It has 

 been called the " wax shears " in the case of the honey bee, 

 as it was supposed to be used for picking the plates of wax 

 out of the wax pockets of the abdominal segments. They can 

 hardly have this function in Bombus, as the species of this 

 genus apparently secrete but little, if any, wax. It has been 

 stated that they make honey pots of wax and that, in some 

 cases, they also build a sort of wax roof over the brood cells. 

 The writer has never observed the wax roofing, but the honey 

 pots are common. As far as the writer has been able to 

 determine, however, the honey pots are not made of wax, 



