1-)1'*^1 Alimeutary Canal of Alt ica Larva 297 



imbedded, it continues around them as a nucleated peritoneum. 

 Their basement membrane is continuous with that of the 

 alimentary epithelium. 



The evagination of these vessels is shown in figure 1«>. 



Their structure and relations make it perfectly clear that 

 any connection which they have with the mid-intestine is 

 entirely secondary. Although there may be two or three 

 cells of the mesenteron which He between them and the hind- 

 intestine, their complete fusion distally with the vessels of the 

 first series, makes it clear that they are appendages of the hind- 

 intestine; and their present point of origin from the ventriculus 

 is due to secondary migration. 



THE PROXIMAL PORTION OF THE ILEUM. 



Proximal and distal ileum. The first division of the hind- 

 intestine, the ileum, may be divided histologically into a 

 proximal and a distal portion. The proximal portion extends 

 from the beginning of the hind-intestine as far as the opening 

 of the bladder. The distal region includes all of the ileum 

 beyond this point. 



The proximal ileum corresponds to the first region of the 

 hind-intestine, and the distal ileum to the second region, as 

 Poyarkojff (1910) considered them in Galeriicella. 



Intima. The primary intima is very thin, but the secondary 

 intima is fairly thick. Neither layer is stained with eosin nor 

 Delafield's haematoxylin , but the primary layer contains brown 

 pigment. 



Epithelium. The epithelium is composed of wide, flat 

 cells, very much smaller than those of the distal region, as are 

 also the round chromatic nuclei, full of densely-packed. coarse 

 granules. The cytoplasm is homogeneous, and usually non- 

 vacular. The epithelium is thrown into small, wavy, pointed 

 folds. " " 



Basement membrane. The basement membrane is well 

 developed. 



Longitudinal muscles. There are about twenty longitudinal 

 muscle fibres, which lie in a continuous connective tissue 

 sheath. Anteriorly they are continuous with the muscles 

 of the ventriculus, and posteriorly they are inserted on the 

 intima at the end of the distal portion of the ileum. 



