18(> THE VITAL FUNCTIONS. 



able for their excessive voracity, even three orders 

 of liepatic vessels are met with.* 



A muscular power has also been provided, not 

 only for the strong actions exerted by the gizzard, 

 but also for the necessary propulsion, in different 

 directions, of the contents both of the stomach and 

 intestinal tubes. The muscular fibres of the latter 

 are distinctly seen to consist of two sets ; the one 

 passing in a transverse or circular, and the other 

 in a longitudinal direction. Glandular structures, 

 analogous to the mucous follicles of the higher ani- 

 mals, are also plainly distinguishable in the internal 

 coat of the canal, more especially of herbivorous 

 insects. i The whole tract of the alimentary canal 

 is attached to the sides of the containing cavity by 

 a membrane, or peritoneum, so fine as to be with 

 difficulty seen, and containing numerous air-vessels, 

 or trachece.\ 



To engage in a minute description of the endless 

 variations in the structure of the digestive organs, 

 presented in the innumerable tribes which compose 

 this class of animals, would be incompatible with 

 the limits of this treatise. I shall content myself, 

 therefore, with giving a few illustrations of their 



* See the Memoires of Marcel de Serres, in the Annales du 

 Museum, xx. 48. 



\ Lyonet. 



X It has been stated by Malpighi and by Swammerdam, and the 

 statement has been repeated by every succeeding anatomist, that 

 almost all the insects belonging to the tribe of Gnjlli, possessed the 

 faculty of ruminating their food; but this error has been refuted by 

 Marcel de Serres, who has offered satisfactory evidence that in no 

 insect is the food subjected to a true rumination, or second mastica- 

 tion, by the organs of the mouth. See Annales du Museum, xx. 51 

 and 364. 



