MUSEUM OF COMPARATIVE ZOOLOGY. 141 



cells are distinguishable from those of the furrows by their greater 

 height, their weaker attraction for dyes, and their vacuolated and gi-an- 

 ular appearance. Moreover, the cell boundaries of this epithelium are 

 gradually lost. Kraepeliu ('87, p. 51) has argued that the elongated 

 cells are the true digestive cells, and that the deeply dyed cells of the 

 furrows are, functionally, liver cells. 



Coecum. — Figure 94 is from a cross section of the coecum at the 

 stage of Figures 84 and 93. The cells are more differentiated here than 

 at any other part of the alimentary tract. They stain uniformly, however, 

 except for a narrow light zone next to the lumen, and all reach to the 

 muscularis. The digestive cells are swollen at their free ends ; the liver 

 cells, on the contrary, are thickest at the base. Figure 83 is from a sec- 

 tion of the proximal part of the caecum of an adult. The changes which 

 the cells have undergone are of a similar character to those experienced 

 by the gastric epithelium, only there has been an exaggeration in this 

 region of the features shown by the stomach. Figure 85 represents a sec- 

 tion near the blind end of the coecum of an adult. The diameter of the 

 tube is smaller here thaif in the section last described, but the inner 

 epithelium is thrown into still higher ridges and more profound furrows. 

 Nearly all of the cells, however, seem to extend to the muscularis. The 

 " liver " cells do not extend so far towards the blind end of the coecum as 

 this region. The cytoplasm is not at all stained. Evidently, here the 

 process of digestion reaches a maximum. The circular muscles of the 

 muscularis are striped, and are developed here to an extraordinary de- 

 gree, and the coelomic epithelium is greatly thickened, another evidence, 

 it seems to me, of the intimate relation of this layer to the muscularis. 

 The number of ridges is not constant in different parts of the alimentary 

 tract of the same individual, and varies somewhat for the same region 

 in different individuals. In sections corresponding in position to Figure 

 83, I have, however, usually found six ridges. 



7. Development of the Funiculus arid Muscles. — It has already (page 

 117) been pointed out that the fixed ends of both the funiculus and 

 muscles originate at a great distance from their position in the adult. 

 Thus the funiculus originates upon the oral face of a young bild. As 

 this bud grows older, the fixed end of its funiculus becomes gradually 

 farther and farther removed from its neck towards the margin, until 

 finally the funiculus is inserted upon the colony- wall at the margin, or 

 even upon the sole. So the retractor and rotator muscles arise together 

 on each side of the polypide and in the angle formed by the colony-wall 

 and the radial partitions. Later (Plate V. Figs. 44, 45, mu. ret. + rot.) 



