DEVELOPMENT OF THE ALIMENTARY CANAL. 423 



anterior extremity, and a mesenteron which is a wide sac 

 opening only by the oesophagus, and entirely disconnected with 

 the proctodseum, which terminates in front in the four large 

 Malpighian tubes. This condition was described by Dohrn, 

 R. Leuckart and others, who regarded it as an anterior stage 

 of development to that described by Swammerdam. 



I have no doubt that the condition so described is a subse- 

 quent stage characteristic of the resting larva. Dohrn says, 

 ' In many Hymenoptera the union of the hind-gut and mesen- 

 teron only occurs at the end of the larval period. It may be 

 observed that if a fairly full-grown Ant larva is hardened and 

 cut through vertically, the mid-gut forms a sac, which is 

 bounded by a layer of large cells, and contains within it 

 about twenty cuticular layers enclosing a brown mass of faecal 

 material ; whilst the hind-gut forms many coils, and is often 

 found to terminate in front in a blind end.' I think it is clear 

 that Dohrn was dealing with a resting larva or young nymph, 

 as the conditions described are similar to those seen in the fly 

 nymph (pronymph stage). The supposition that, in the feeding 

 larvae of the Hymenoptera, a blind mid-gut unites with 

 the hind-gut after the functional activity of the organ has 

 ceased, and just before the whole alimentary canal under- 

 goes histolysis, is scarcely probable ; on the other hand, it is 

 extremely probable that, as in the fly nymph, the union between 

 the parts of the alimentary canal becomes very narrow (see 

 PL XXV., Fig. i), or may even become a mere fibrous cord. 

 It is possible that the whole of the Malpighian tubes and the 

 metenteron are expelled through the short, wide intestine in 

 the Bee nymph, and that the new metenteron and new Mal- 

 pighian tubes are developed, as in the fly nymph, from the 

 saccular mid-gut. 



Leuckart, in his great paper [20] on the development of the 

 Pupiparse, does not represent the alimentary canal as discon- 

 tinuous ; but in a previous note* he announced that he had 

 discovered a similar want of continuity in the nymphs of these 

 insects; again, I think he had to do with a subsequent and 

 * 'Bull. Acad. Sci. Bruxelles,' xxi., 1854, pp. 851, 852. 



