DEVELOPMENT OF THE ALIMENTARY CANAL 425 
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 proctodeum, 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 
stomodzum 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 stomodzum 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 
stomodeum. I have been unable to determine that it is 
developed from the original proctodzum, but I think that it 
most probably is, and that only a part, probably a diverticulum, 
