REPORT OF THE SOCIETY 39 



which especially concerns us being 12-13 mm. They resemble the Andrenidae 

 somewhat in general form, but differences in character, particularly in their 

 wing venation, enable the tw^o genera to be easily separated. 



One peculiarity, which has given the Colletes an unique place among the 

 Apidae, may be appropriately mentioned here. Alone among all other bees, they 

 line their cells with a viscous substance, which on hardening forms a silky mem- 

 brane, a sort of transparent skin. This fact has given rise to the German name, 

 "Silk Bees." 



The biology of these little insects is extremely interesting, the construction of 

 their nests in particular presenting important variations. i\t the commence- 

 ment of my studies on bees, I became accustomed to look upon the construction 

 and disposition of the cells as entirely a generic character. Different observations 

 have proved to me, howe\'er, that the contrary is the case. I cite as an example 

 Angochlora pura, which builds its nest in old stumps and constructs the cells with 

 sawdust, whilst another Angochlora species builds in the earth, using sand. 

 Then again, while the Anthophorae build their nests as a general rule in sub- 

 terranean galleries, Anthophora terminalis utilizes the branches of sumach, or 

 the trunks of trees. The Colletes furnish another example of the diversity which 

 can exist in the next construction of different species. 



According to the forms of the galleries, three forms of construction can 

 be distinguished among them: 



1. A vertical pit, with side branches. 



Ex. C. compacta and C. inaeqicalis in N. America. 



2. A horizontal gallery with vertical branches. 

 Ex. C. succincta in Europe. 



3. A simple horizontal gallery. 



Ex. C. hirta floralis and marginellus and the majority of the other Euro- 

 pean species. 



This latter form of construction is remarkable for its ingenuity, the cells are 

 laid down one after the other, exactly similar to those of a Megachile, or to give a 

 simile of a more ordinary nature, like the cartridges in the magazine of a repeating 

 rifle. The cover of each cell forms the floor of the following one, and in this way 

 the bee reduces the preliminary labour to a minimum, and can concentrate all 

 her attention in harvesting pollen and oviposition. What gradation, "what 

 progress is realised from one species to the other." It is a magnificent example of 

 evolution, and a confirmed follower of Darwin would not lose the opportunity of 

 drawing weighty conclusions therefrom. The explanation is simple indeed. Our 

 indigenous Colletes are still in the last rank of the genus. The digging of a deep 



