270 



CHARLES RUSSELL BARDEEX. 



(Fig. 5, ). As pointed out by lijima, however, this last process 

 is slow, and it is only at a comparatively late period in develop- 

 ment that the intestinal epithelium assumes the structure charac- 

 teristic of the adult. Whether the intestinal epithelium is differ- 

 entiated at a very early period and then preserves its specificity, 

 like the surface epithelium, or is added to by constant additions 

 from the parenchyma, it is difficult to decide. The former 

 view seems to me perhaps more probable. It must be stated in 



Fir,. 5. Sections illustrating the development of the intestinal epithelium. Mag- 

 nification, 540 diameters. 



a. Flat cells seen in embryos at the time of the development of the permanent 

 pharynx. 



b. Cells beginning to project toward the lumen of the intestine in an embryo in 

 which the nervous system has just become clearly visible. 



c. d. Intestinal cells undergoing direct division during regeneration in the adult. 

 e. Cells bordering on the intestines. In one cell a mitotic figure is visible. 



this connection, however, that the parenchyma cells bordering 

 on the intestines show active proliferation by mitosis during em- 

 bryonic development as well as during regeneration (see Fig. 



Myoblasts become numerous at about the period of the forma- 

 tion of the anlage of the permanent pharynx (Fig. 6, rt). They 

 are very large cells and apparently are derived from cells of the 

 type shown in Fig. 4, c, many of which have more vesicular nu- 

 clei than there shown. The myoblasts seem to divide by indirect 

 division. From those lying next the basement membrane of the 

 epithelium is derived a syncytium, a portion of which is shown 

 in Fig. 6, /;. In this the surface musculature is developed. It is 

 probable that a separate syncytial sheet exists for each layer of 

 musculature. Other myoblasts give rise to the muscle fibers 

 which run through the parenchyma in various directions. 



