120 INTERNAL ANATOMY OF INSECTS. 



sessile and imited a ; and in Tabanus sessile a\\djixed b . 

 It is remarkable that in some of this Order the reverse 

 of what usually happens the alimentary canal appears 

 to be much longer in the larva than it is in the imago ; 

 in Musca vomitoria, its length in the former is two inches 

 and a quarter, while in the latter it is only one inch and 

 one third . A singular organ distinguishes the imago 

 of this species, the use of which appears not to be disco- 

 vered. It succeeds the rectum, and has on each side 

 two short club-shaped appendages, open at the end, 

 which receive tracheae, and terminate in a short piece 

 that opens into the anus d . 



In Hippobosca and its affinities the canal in question 

 differs from that of other Diptera, in having no food-re- 

 servoir ; in other respects it resembles it e . 



From the above statement it appears that the princi- 

 pal character which distinguishes those that take their 

 food by suction, from those that masticate it, is the faculty 

 with which they are furnished by means of an ample 

 crop, honey-stomach, or food- reservoir, of regurgitating 

 the food they may have stored up. Another distinction 

 still more striking, which will appear more evidently 

 hereafter, is to be seen in the saliva-sewetors with which 

 the suctorious tribes are furnished, to be found in very 

 few masticators, by which they are enabled to render 

 the juices more fluid and fit for suction. 



The only insect amongst the Aptera whose alimentary 



a Ramdohr, Ibid. t. xx./. 1. G.f. 2, 3. L. * Ibid. t. xxi./. l.D. 



c Ibid. 172. d Jbid. L xix./. 2. KL. This 



organ seems analogous to that with four retractile fleshy horns, ob- 

 served by Reaumur and De Geer in other species of Muscidce. 

 Reaum. iv. t. xxviii./. 13. a t s. De Geer vi, t. iii./. 18. c> d. 



c Ramdohr /. xxi./. 6. 



