374 PHYSIOLOGY. 



probable that in the other grasshoppers such vessels will be found, as 

 well as in other voracious insects, which, as such, more require excretory 

 organs ; whereas in temperate insects, and such as feed upon highly 

 elaborated finer substances, as well as haustellate insects from the 

 greater preparation of their food, and its consequent perfect quality of 

 assimilation, the excretory organs would be wholly superfluous. Where- 

 fore then, it might be objected, have the voracious caterpillars and 

 larvae no urinary organs? To which we might reply, that it must not 

 be forgotten that larvae stand upon a much lower grade of animal deve- 

 lopment than perfect insects, and that they therefore do not display so 

 great a separation and division of their organs ; if the anus be wanting 

 in some instances, how much more likely are the urinary organs to 

 be deficient ? and, besides, the majority of caterpillars have other 

 excretory organs, viz., the spinning vessels, which take up from the 

 body much useless matter. The unimportance of the urinary organs to 

 the nutriment of larvae explains their deficiency in those cases in which 

 the beetle exhibits them ; at least in the larva of Calosoma sycophanta 

 I have not observed such organs. 



If, then, the biliary vessels be neither exclusively liver nor exclusively 

 kidneys, it remains to be determined what their function is. To arrive 

 at this we look around us for analogous forms in other animals, and 

 immediately discover the paired casca of birds. These organs, which 

 Cams * even wished to compare to biliary vessels, diverge in one 

 respect by their frequently considerable shortness (for example, in all 

 the diurnal birds of prey), and in a second respect by their contents 

 differing so much from that of the biliary vessels of insects ; they are 

 also of a similar structure with the intestinal canal, which is not the 

 case with the biliary vessels. But it is remarkable that the parallel 

 orders of birds and insects exhibit some approximation in the length of 

 these organs, for the biliary vessels are likewise very short in the car- 

 nivorous Carabodea, and if not exceedingly long yet they are very 

 numerous in the herbivorous grasshoppers and Grylli, which I com- 

 pare with the gallinaceous birds, into the detail of which I shall go 

 below. We might therefore indicate, if not a strict analogy, at all 

 events a certain approximate relation between these appendages of 

 the intestinal canal. 



Besides these paired caeca of birds we find no other appendages to 



' Zootoinic, p. 388. 



