LETTER XL! 
INTERNAL ANATOMY AND PHYSIOLOGY 
OF INSECTS, CONTINUED. 
SECRETION. 
HAVING given you so full an account of the system of 
digestion in insects, I am now to say something concern- 
ing their secretions, and the organs by which they are 
elaborated. Though no individual amongst them per- 
haps secretes so many different substances as the warm- 
blooded animals ; yet in general the Class abounds in 
secretions perhaps as numerous and extraordinary as in 
the last-mentioned tribes, to some of which a few of them 
are analogous, while others are altogether peculiar. We 
know little or nothing of the mode in which the process 
of secretion in insects is accomplished ; in most cases we 
cannot even discover, except in general, whence the se- 
creted substance originates; and in others, though we are 
able to trace the vessels that contain it, we are often in 
the dark as to their structure. — Cuvier, as has been be- 
fore hinted, from not being able to detect any thing in 
them like glands, and from their being constantly bathed 
in the blood or nutritive fluid, conceives that they sepa- 
rate the peculiar substances they contain, by imbibition 
