120 INTERNAL ANATOMY OF INSECTS. 
sessile and united » ; and in Tabanus sessile and i yfa«/ 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 imajjo ; 
in Muscu vomitoria, its length in the, former is two inches 
and a quarter, while in the latter it is only one inch and 
one third c . 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 trachea, 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 
Avith which they are furnished by means of an ample 
crop, honey-stomach, or food- reservoir, of regurgitati?ig 
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-secretors with which 
the suctorio?is 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 Aptcra whose alimentary 
a Ramdohr, Ibid. t. xx.. f, 1. G.f. 2, 3. L. b Ibid. t. xxlf. 1.2). 
c Ibid. 172. d Ibid. t. xix./ 2. K L. This 
organ seems analogous to that with four retractile fleshy horns, ob- 
served by Reaumur and De Geer in other species of Muscidcc. 
Rcaum. iv. /. xxviii./. 13. a, s. De Gecr vi. t. hi./. 18. c, d. 
e Ramdohr /. xxi./. 6. 
