of our Britlsli Hymenoptera. 171 



9tli. Somewhat spirally-grooved hairs, dilated and 

 flattened at the extremity, sometimes very 

 short (on the inner side of the hind tibite of 

 Andrena, Megachile, &c.) (fig. 13). 



The interesting question now remains as to what the 

 use of these peculiar hairs can be. If my observation is 

 correct that they exist only in the AntliopJiila, then I 

 think there is a strong inference that they are of some 

 use in the collecting of pollen, although they equally 

 occur on the parasitic bees, such as Nomada^ &c. It is 

 also remarkable that the parts specially adapted for col- 

 lecting pollen should bear such differently-shaped hairs in 

 various species. Thus the pollen hairs of the brush of 

 Megachile, with their long spiral shapes, would hardly 

 seem to be useful for the same purpose as the flexuous 

 and branched ones of the brush of Chelostoma. Still we 

 know that it is by means of these brushes that they carry 

 home most of their pollen, and no doubt in some Avay each 

 species finds its own brush especially serviceable. What 

 I should much like to find out is, whether the species that 

 frequent the same flowers have similarly-formed pollen 

 hairs. I have been trying to arrive at this by the exami- 

 nation of the pollen grains on the hairs, but in many 

 cases I find two or more kinds present, and my knowledge 

 of their shapes is not sufficient to knoAV wdiat species they 

 belong to. They seem to stick to the hairs anywhere, 

 sometimes on the sides, and sometimes on the points of the 

 branches. I hope that by further study of this subject the 

 uses of these characters may be arrived at, as I feel sure 

 they must in some way play an important part in the 

 economy of the insects under consideration. 



I have found a quarter-inch power the most usefiil for 

 examining the hairs. 



Since reading the foregoing, I have noticed that the 

 hairs on the scopa? of the $s of the Andrenidcs seem to be 

 arranged on a definite plan, and that this arrangement is 

 similar in all the species. The outer side of the tibi« is 

 covered with simple, or in some cases branched, hairs, 

 such as those figured in figs. 4 or 7 ; the inner side, or side 

 towards the body, is covered with spiral hairs with dilated 

 apices, like those in fig. 13 ; between the sides, on the edges, 

 is a series of hairs, such as those figured 10, 11, 12, 12a, 

 varying much according to the species. The arrangement 

 of the hairs on the tarsi seems to be somewhat similar. 



n2 



