SOCIAL ECONOMY. o27 
equal length. Besides these, we find the lower end 
of the bowel, containing all the undigested food and 
excretions which have accumulated there since the 
larva first began to feed. The reason of this singular 
arrangement will be obvious on a little consideration. 
Placed as the larva is, vertically, in a closely fitting 
cell, which it cannot leave, and from which there 
could be no drainage except by the side of its body, 
it is necessary to provide against this contingency, 
and also against the decomposition of the excreted 
matters. The object is effected, as usual, in the 
simplest possible way: the excreta are retained not 
only within a membrane, but within the body of the 
larva, secured, as far as may be, from chemical in- 
fluences, and from becoming a source of injury to the 
helpless larva. Thus :—in the larva of the wasp the 
bowel does not open by a vent externally, but to f/ 
minates in a blind pouch, which receives all th 
excretions and the undigested residue of the food. 
The smallest atom of a larva has often a dark speck 
visible through its skin. This grows larger, with 
the growth of the larva, till the second moulting, 
when it is cast off with the skin, as a hard black 
mass closely invested with the membrane which 
formed the end of the bowel. On examination with 
the microscope, this mass is found to consist of scales, 
hairs, and other fragments of insects, hairs of vege- 
tables, and other substances less easy of recognition. 
From this inventory it would seem that, from the 
, earliest period of their existence, these little mites 
Y are fed on chopped insects. An observation of 
Wildman confirms this inference, and shows that 
the mandibles of the larve are meant for real work, to 
Q 2 
