ANATOMY AND PHYSIOLOGY. 171 
at about thirty lines. But this measure must be 
accepted only as a very rude approximation, on 
account of the yieldmg nature of the tube, which | 
may be stretched to various lengths by different 
observers. The spiral makes about two complete 
turns in its passage through the abdomen. Speaking 
of insects generally, the length of the alimentary 
canal varies in each family inversely as the digestible 
nature of their food. Predaceous insects, that is to 
say those which live on animal food, have, as a rule, 
shorter alimentary canals than vegetable feeders, 
because, as a rule, their food is more easily digested. 
But this rule has numerous exceptions. If the food 
be easy of assimilation, whatever its nature, animal 
or vegetable, the canal is short and simple, but if it 
be more refractory the canal is longer, and its ap- 
pendages are more complex. The food of the wasp, 
though mixed, is generally fluid and easy of diges- 
tion, and the alimentary canal of the wasp, accord- 
ingly, as we have traced it, is short and simple.* 
THE REPRODUCTIVE SYSTEM comes next under 
consideration. There is no great difficulty in the 
anatomical examination of these parts, none but 
what patience and practice will surmount. The 
several organs are large enough to be easily recog- 
nized, when we have once learned where to look for 
them, and how to disentangle them. It is in the 
morphological interpretation of what we see that 
the chief difficulty and the great interest of the 
inquiry lic. I must refer to Burmeister’s elaborate 
* See this question fully examined and illustrated, ‘ Cyclop. Anat. 
Phys.’ Vol, Il, pp. 966—973. 
