210 THE VITAL FUNCTIONS. 



the existence and developement of the gizzard, 

 and consequently also to the nature and bulk of 

 the food. Vessels of this description are, indeed, 

 constantly found in insects ; but it is only where 

 a gizzard exists, that two sets of these secreting 

 organs are provided ; and in some larvae, remark- 

 able for their excessive voracity, even three 

 orders of hepatic 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 dif- 

 ferent 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 direc- 

 tion. Glandular structures, analogous to the 

 mucous follicles of the higher animals, are also 

 plainly distinguishable in the internal coat of the 

 canal, more especially of herbivorous insects. | 

 The whole tract of the alimentary canal is at- 

 tached to the sides of the containing cavity by a 

 fine membrane, or peritoneum, containing numer- 

 ous air-vessels, or trachecB.\ 



* See the Memoirs of Marcel des Serres, in the Annales du 

 Museum, xx. 48. 



f Lyonet. 



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

 the statement has been repeated by every succeeding ana- 

 tomist, that almost all the insects belonging to the tribe of 



i 



