DEVELOPMENT OF THE ALIMENTARY CANAL. 42$ 



surface views to distinguish the lumen in the embryonic stages 

 of development. 



Although there are no figures representing actual sections 

 or dissections in which the Malpighian tubes are seen opening 

 into the proctodseum, Graber has, as has been already stated, 

 figured them opening into the mesenteron [114, Taf. III., 

 Fig. 27], as my own observations have led me to conclude 

 they do. 



The difficulties which are met with in the investigation of 

 the development of the alimentary canal in the embryo are 

 very great, and it is rarely a single section gives any complete 

 demonstration as to the manner in which the several parts of 

 the alimentary canal are related to each other. 



The following account of the development of the alimen- 

 tary canal in the embryo agrees in many important particulars 

 with that given by Weismann. 



The fore-gut is primarily an invagination of the epiblast ; 

 it remains from the first without convolutions, and is a hollow 

 epithelial tube ; the crop is formed as a sac which grows 

 from its ventral wall. All the parts developed from the 

 stomodasum have in their definitive stage a pavement epithe- 

 lium, and a well-marked chitinized intima. 



The mid-gut orginates as an ovoid sac enclosing yelk cells ; 

 it is so large that in the nymphoid embryo it occupies the 

 greater part of the interior of the body. The proventriculus 

 is formed from a ring of cells attached to the epithelial wall, by 

 which the posterior blind end of the stomodseum is enclosed. 

 The Malpighian vessels are developed in relation with the 

 posterior extremity of the mesenteron. 



The metenteron (mihi) arises from the hypoblast, and, like 

 the mesenteron, has a columnar epithelium in its definitive 

 stage of development. 



The rectum of the larva is very short; it has a structure 

 precisely similar to that of the parts formed from the 

 stomodseum. I have been unable to determine that it is 

 developed from the original proctodseum, but I think that it 

 most probably is, and that only a part, probably a diverticulum, 



