Transactions of the Royal Society. 333 



chyle, in the first instance, from the internal surface of the alimen- 

 tary canal, and thence conveying it to the various parts of the 

 body ; nor is this opinion, however improbable it may appear, 

 entirely gratuitous. No difficulty, I apprehend, attaches to the 

 supposition that such an absorption may take place, seeing that 

 innumerable minute ramifications of the tracheae penetrate the in- 

 testinal canal in every part ; nor does there seem any difficulty in 

 admitting that the insect may, by the power of exhausting the air 

 from individual tracheae, draw on the absorbed fluid towards those 

 two lateral tracheal tubes, which are apparently a general me- 

 dium 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 whatever means the air itself is for- 

 warded from the same point to the most distant parts 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 after 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 con- 

 nected 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 importance. 



u 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 intestines ; 

 for, if the blood be conveyed to the several parts by previous ge- 

 neral diffusion through the interior of the body, and then by ab- 

 sorption into the substance of particular organs, as the hepatic 

 tubes, the vesiculae seminales and the ovaries ; how does it happen 

 that the bile, for instance, does not transude through the coats of 

 the same, vessels, the pores of which have admitted the blood from 

 which it has been formed ? It may be answered, that the altera- 

 tion which the blood undergoes 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 ento- 

 Vol. XX. 2 A 



