ANDRENA. 
205 
this subfamily its collective designation, making the 
other genera thus converge to it as to a centre. He 
took its elliptical form as typical. Indeed, it is remark¬ 
able how very judiciously this was done, for it is a form 
not apparent among the normal bees excepting in two 
exceptional cases, the one upon tha frontiers of this 
subfamily, in almost debatable land, where the last of 
the Andrenidce and the first of the Apidce seem almost 
to melt into one another; and in the other case, in the 
parasitical Nomada , whose parasitism is in every in¬ 
stance, but one only, restricted to the first subfamily. 
A different type of form prevails amongst the Apidce, 
upon which I shall have subsequently occasion to speak. 
These insects are not distinguished for any elaborate 
economy. Varying in the species, some prefer vertical 
banks, others sloping undulations, and again others ho¬ 
rizontal flat ground or hard down-trodden pathways. 
Some burrow singly, and others are gregarious, col¬ 
lected in great numbers upon one spot. They are, 
perhaps, the most inartificial burrowers of all the bees. 
Their tunnels vary from five to nine or ten inches in 
depth, and in some species they are formed with other 
small tunnels slanting off from the main cylinder. The 
sides and bottom are merely smoothed, without either 
drapery or polish. The little cells thus formed are then 
supplied with the usual mixture of pollen and honey 
kneaded together, which in the larger species forms a 
mass of about the size of a moderate red currant, its 
instinct teaching it the quantity necessary for the nur¬ 
ture of the young which shall proceed from the egg 
that it then deposits upon this collected mass of food. 
The aperture of each little tunnel is closed with par¬ 
ticles of the earth or sand wherein the insect burrows, 
