310 CLASS VIII. 



consisting of five joints. The last joint has two claws and two or 

 three plane elevations or cushions (see above, p. 252). 



The digestive organs of Diptera consist of a wide bent stomach 

 of moderate length, a small intestine, and an oval oblong large 

 intestine. The salivary vessels vary in the different genera of this 

 order. The oesophagus has a dilatation (ingluvies, crop, see above, 

 p. 254) ; it is a bladder of various form, either simple, or pro- 

 longed into two or more divisions, and communicating with the 

 oesophagus by a long narrow tube (often with its lowest part close 

 above the stomach). In larvae the tube is shorter and inserted into 

 the oesophagus higher up. In by far the greater number of Diptera 

 this bladder is present ', in the family of the Pupiparce it is wanting 

 (comp. BAMDOHR, Abhandlung. ub. die Verdauungswerkzeuge d. Ins. 

 Tab. xix. xxi, and pp. 170 185). TREVIRANUS named this organ, 

 which is also found in the Hymenoptera and Lepidoptera, sucking- 

 bladder ; he attributed to it a power of expanding, in consequence 

 of which the air in the oesophagus is ratified, whilst, to fill this 

 partial vacuum, the fluid in which the extremity of the sucker is 

 planted ascends as if pumped up, (Verm. Schr. n. s. 110). The 

 Herrdptera and the Pulicidce do not possess this bag ; on the other 

 hand, such a crop is present in the Orthoptera, which do not suck, 

 and according to LEON DUFOUR in (Edemera amongst the Coleoptera 

 (Ann. des Sc. nat. m. 1824, p. 484, PL 30, fig. 7). The name of 

 food-bag, which was given by RAMDOHR to this part in Diptera, is 

 therefore more appropriate than that of sucking-bladder. When 

 flies that have long fasted suck their full of milk, according to the 

 investigations of HUNTER, milk penetrates into this bladder. By 

 pressure of the abdomen, and apparently also by contraction of the 

 muscular walls of the bladder itself, the food is afterwards brought 

 back from this diverticulum or reservoir of nutriment to the sto- 



1 According to the anatomical investigations of SCHRCEDER VAN DER KOLK it seeme 

 to be wanting in the larva of (Estrus ; but at the same point where ordinarily the 

 tube from the food-bag [the name given by RAMDOHR to the sac] is inserted into the 

 oesophagus, two tortuous canals are seen, which divide at their other extremity into 

 two branches, which are distributed to the adipose body. Memoire sur V Anatomic 

 et la Physiologis du Gastrus equi. Amsterdam, 1845, pp. 29, 30. PI. m. fig. i, b, s, s. 

 BAMDOHR has figured four such appendages above and near the stomach in the larva 

 of Musca vomitoria, which would seem at their other extremity to be implanted into the 

 salivary vessels, and in the perfect insect to disappear. Tab. xix. fig. I. M, M, M, M. 

 Do these vessels form, perhaps, a second apparatus for secreting saliva ? 



