HENRY J. FRANKLIN. 233 



but are constructed of pollen grains held together by some 

 sort of glue, or cement. This cement may be propolis. It 

 is interesting, in this connection, to note that Snodgrass, in 

 his paper on the anatomy of the honey bee, states that he 

 "has watched the bees take the wax from their abdomen 

 and, in these observations, they always poked the wax plates 

 loose with the ordinary hairs or spines of the tibiae or tarsi and 

 then, by means of the feet, passed them forward beneath the 

 body." 



In the opinion of the writer, Kirby came the nearest to 

 suggesting the true function of these "wax shears," when 

 he supposed them to be used in preparing the pollen masses 

 borne by the corbiculae. Some of the pollen appears to be 

 scraped off from the spinous brushes, on the inner faces of 

 the middle and hind matatarsi, by the comb of stout spines 

 on the distal end of the hind tibia of the opposite side. This 

 comb guides the pollen into the cleft, above described, be- 

 tween the tibia and the metatarsus. The crushing of the 

 pollen grains in this cleft, which may, perhaps, be appro- 

 priately called the pollen mill, probably provides the viscid 

 fluid necessary for holding the rest of the pollen together 

 in the balls which are formed on the outer faces of the hind 

 tibias. 



Neither Psithyrus nor the males of Bonibus have any notice- 

 able posterior basal extension on their hind metatarsi (fig. K 

 shows this extension of the Bombus queens, while fig. I shows 

 the lack of it in the Psithyrus females). 



In the males, the length of the hairs, borne on the hind 

 borders of the posterior metatarsi, varies greatly between 

 the different species. This comparative length is very con- 

 stant within species limits and also, to a greater or less ex- 

 tent, within group limits. It is, therefore, of much value in 

 classification. This hairy fringe is always long in the males 

 of Psithyrus and of Bombias and of the Kirbyellus group. It 

 is always short in the males of the Borealis, Dumoucheli and 

 Terrestris groups. In the Pratorum group, it is variable. 

 In the females of all Bo7nbus groups, this fringe is rather 

 long toward the base of the metatarsus, but rather short 



TRANS. AM. ENT. SOC, XXXVIII. (30) 



