242 Rev. F. D. Morice on Armatures, etc. of Andrena. 



views (14(1, 15a) as a spiniform, development of the 

 geniculation (x) answering to the lohatc developments in 

 9a, etc. The very short and broad-based portion of the 

 segment beyond these hooks or spines is an exaggeration 

 of such a process, widening from the apex to the genicula- 

 tion, as we see in Figs. 9^ and 1G?>. This hypothesis to 

 my mind accounts satisfactorily for all tlieir peculiarities, 

 and brings them into an intelligible relation with the 

 other types that we have examined. 



One other question I will raise, and endeavour to 

 answer with a hypothesis. Why does the pilosity of this 

 segment throughout the genus tend so markedly to a 

 lateral development on each side of the geniculation ? 

 Because, I will venture to reply, the process with its 

 pilosity serves to close from behind that gap between the 

 stipites in which lie the sagitta;. Since the process from 

 the geniculation towards the apex gradually approaches 

 nearer to the back of these organs, the gap which the 

 pilosity has to shelter gradually diminishes, and the 

 pilosity can diminish also. It is at the geniculation that 

 the process is most distant, both from the stipites and 

 from the sagittse, and it is precisely there that the 

 pilosity seems most concentrated and developed. 



I have little doubt that the general outline of the 

 process as seen ventrally, including its pilosity, is deter- 

 mined in each species by that of the cavity at the back of 

 the armature which it screens. But to prove or disprove 

 this hypothesis completely would require a further investi- 

 gation, on which I cannot enter here. 



One more remark I will make, viz., that in Andrena as in 

 other genera, though the armature as a whole is concealed 

 and hairless for the most part, some pilosity (very little, 

 however, in this genus) is developed on the apex of the 

 stipes. This pilosity springs from what, but for the crease, 

 would have been the ventral surface of the stipes. Owing to 

 the crease, it is diverted or transferred to form part of the 

 doo'sal clothing of the insect. A few hairs also exist at the 

 bases of the stipites posteriorly, which originate as ventral 

 and remain so, combining with [the pilosity of the 8th 

 segment, and (I may add) with the apical pencils of the 7 th, 

 to close the gap, of which so much has been said, at the 

 back of the armature. Here, as throughout their whole 

 structure, the parts we have considered seem, as far as we 

 can interpret them, to be accommodated one to another 



