191S] Alimentary Canal of Altica Larva 295 



Replacement cells. The replacement cells are of the same 

 type and arrangement as in the j^receding region. 



Basement membrane. The basement membrane is of the 

 same character as in the preceding region. 



Circular muscles. The condition of the circular muscle 

 fibres is the same as in the preceding region. 



Longitudinal muscles. The longitudinal muscle fibres are 

 continuous with those of the preceding region. They are more 

 numerous, as the fibres split up more or less at the point of 

 junction between the two regions. 



The musculature of the two regions of the ventriculus is 

 shown in figure lo. 



The Hind Intestine. 



THE TRANSITION BETWEEN THE MID-INTESTINE AND THE 

 HIND-INTESTINE. 



Striated border. The striated border stops with the end of 

 the mid-intestinal epithelium. It is very faint and feebly 

 developed, as is characteristic of the whole posterior portion 

 of the second division of the ventriculus. 



Intima. A chitinous intima originates with the epithelium 

 of the hind-intestine. The primary intima is very thin, the 

 secondary somewhat broader. Neither layer is stained by 

 eosin nor by Delafield's heematoxylin. 



Epithelium. There is a sharp break between the epithelium 

 of the mid-intestine and that of the hind-intestine. The 

 epithelial cells of the mid-intestine do not differ markedly 

 from the normal as the transition area is approached, save 

 that the replacement cells become very numerous, and tend 

 to form small nests or nidi, instead of occurring singly. At 

 the extreme end of the mid-intestine, the cells lose their columnar 

 character, the cell divisions become very indistinct, and the 

 replacement cells are abundant. The epitheHum of the hind- 

 intestine is clearly separated from that of the mid-intestine. 

 The cells, at first narrow, become higher and wider, and shortly 

 merge into an epithelium perfectly typical of the proximal 

 division of the ileum. The cytoplasm is vacuolar and very 

 fibrillar. 



The transition area is shown in figure 14. 



