1826.] Thilosophical Transactions for 1825, Tart II. 211 



form, though of less extent than the precedinar, is situated imme- 

 diately behind the root of the middle leg; the third, which is 

 still less than the second, is situated immediately behind the 

 root of the posterior leg ; from the fourth to the tenth inclusive, 

 are situated near the terminations of the corresponding dorsal 

 segments of the abdomen. 



The stigmata, taken generally, are not the terminations of 

 single tubes ; very frequently two and even more tracheae origi- 

 nate from the same stigma ; and very soon after the commence- 

 ment, one or even two of these tracheae subdivide into numerous 

 branches, which follow as nearly as may be the direction of the 

 original tubes. 



"It is generally understood, that the tracheae of insects pene- 

 trate each organ and every part of the body ; and certainly the 

 case is such in the instance before us. Thus, in that brush of 

 capillary yellow tubes supposed to constitute the hepatic system, 

 the total number of which amounts to 150 or 200, there is reason 

 to believe that each tube is accompanied by a distinct trachea 

 coiled round it in a long spiral. Again, the two medullary cords 

 which connect the several ganglions of the nervous system, are 

 in their natural state united together by means of the branches 

 of a tracheal tube which runs between them ; a similar tube being' 

 attached to the exterior edge of the cords ; and the surface of 

 what may be called the brain of this insect is as beautifully 

 characterized by the ramifications of the tracheae which pervade 

 it, as the surface of the pia mater of the human brain by the 

 blood vessels which penetrate that membrane in every direction. 



" In meditating on the difficult problem of the sanguineous 

 circulation of insects, it has forcibly occurred to me, that the 

 tracheae may possibly be the instruments of such a circulation ; 

 absorbing the blood or the chyle in the first instance from the 

 internal surface of the ahmentary 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 intestinal 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 trachete, draw 

 on the absorbed fluid towards those two lateral tracheal tubes, 

 which are apparently a general medium of communication 

 between all the other tracheiB of the body. And when once the 

 blood has reached this supposed point of its course, it is mani- 

 fest, that by whatever means the air itself is forwarded from the 

 same point to the most distant parts of the body, by a modifica- 

 tion of the same means, the blood may be forwarded to the same 

 part ; and the elegant proposition of Cuvier, that ** the blood 



r2 



