LETTER XLI. 



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 



