ANATOMY AND PHYSIOLOGY. 163 
bag. This is the lower end of the cesophagus, dilated 
into a pouch or crop, which has been also called the 
sucking-stomach. ‘The last name is ill chosen, for 
the crop has not any power of self-dilatation by which 
it can suck: it can only follow the motions of the 
abdominal walls, like a flaccid bladder. It is merely 
a receptacle in which the juices on which the wasp 
lives, or the honey which the bee gathers are col- 
lected, not digested. The want of any digestive 
power is apparent from the structure of the organ. 
It has no thick glandular lining, and there are few 
tracheze on its outer surface. Glands and _ blood- 
vessels, or their equivalents, are just as necessary to 
secretion in the insect as in the Vertebrate economy. 
In their absence we may safely infer that the con- 
tents of the bag are not subjected to any active vital 
process, but that they are returned from its cavity 
much as they entered it. 
Above, this bag is continuous with the cesophagus, 
which by gentle traction may be withdrawn from 
the thorax as a simple tube, of uniform diameter, 
mainly composed of longitudinal fibres. In the 
mouth the muscular fibres are marked with trans- 
verse striz, the physiological meaning of which has 
been already fully explained. But as the pharynx, 
or throat, narrows into the oesophagus, these are 
replaced by involuntary fibres, arranged in longitu- 
dinal bands. On the walls of the sac which we have 
been describing, into which the oesophagus gradually 
expands, the appearance of bands and of distinct 
muscular fibres is lost; and the sac appears like a 
membranous bag, with as little power of independent 
contraction as of dilatation. 
M 2 
