+:22 Dr. Kidcl on the Analomij 



mitting that the insect may, by the power of exhausting the 

 air from individual tracheae, draw on the absorbed fluid to- 

 wards those two lateral tracheal tubes, which are apparently 

 a general medium of communication between all the other 

 tracheae of the body. And, when once the blood has reached 

 this supposed point of its course, it is manifest that by what- 

 ever means the air itself is forwarded from the same point to 

 the most distant pai'ts of the body, by a modification of the 

 same means the blood may be forwarded to the same part ; 

 and the elegant proposition of Cuvier, that " the blood being 

 incapable of going in search of the air, the air goes in search 

 of it," will still remain inviolate. 



If it should be argued that the tracheae are not found 

 charged with blood alter the death of the animal, it may be 

 answered, that neither are the arteries in the higher orders of 

 animals found charged with blood after their death. However, 

 I have actually seen some of the ramifications of those tracheae 

 which are connected with the caeca distended with a fluid of 

 the same colour as that found in those organs; and though I 

 have only witnessed this fact in two instances, yet such a fact, 

 even singly taken, must be allowed to be of considerable im- 

 portance. 



Of one thing I am certain, that, after careful observation, I 

 have never found the abdominal viscera, I will not say bathed, 

 as some authors of credit have expressed themselves, in the 

 nutrient fluid which is supposed to have transuded through 

 the coats of the intestines ; but I have not even found them 

 lubricated by a greater proportion of moisture than lubricates 

 the intestines of the higher classes of animals. 



There is another difficulty which occurs to the hypothesis 

 of the transudation of the chyle through the coats of the in- 

 testines ; for, if the blood be conveyed to the several parts by 

 previous general diftusion through the interior of the body, 

 and then by absorption into the substance of particular organs, 

 as the hepatic tubes, the vesiada: seminales, and the ovaries ; 

 how does it happen that the bile, for instance, does not trans- 

 ude through the coats of the same vessels, the pores of which 

 have admitted the blood from which it has been formed? It 

 may be ansAvered, that the alteration which the blood under- 

 goes in the several organs, changes its properties to such an 

 extent, as to render it incapable of repassing through the pores 

 which admitted it. I cannot of course presume to say that 

 such is not the case ; and I am aware that many entomologists 

 will be surprised at, and perhaps disinclined to listen to, the 

 opinion here advanced with respect to a sanguineous circula- 

 tion in insects ; but I nevertheless hope that the opinion will 



not 



