STUDIES ON CILIATED CELLS 223 



degree of differentiation of iron-haematoxylin, as a single dark 

 line beneath the cuticle. The transparent zone is about one 

 half the height of the cuticle and is marked off distinctly from 

 the cytoplasm proper. Chondriocontes are also visible; their 

 arrangement is similar to that described above for Anodonta. 

 Centrosomes and mitotic figures are easily recognizable; two- 

 or poly-nucleated cells also occur. 



5. The hepatic duct of Helix. The epithelium in this region 

 is composed of ciliated cells with interspersed glandular- and 

 non-ciliated columnar cells; in approaching the gland proper 

 non-ciliated cells increase in number. The cilia pass, as usual, 

 through the cuticle in order to connect with basal corpuscles, 

 which appear as minute granules and form, viewed from the 

 surface, linear series running parallel with one another (figs. 10, 

 11). Sometimes the course of the chondriocontes is so regular, 

 that they form a sort of palisade (fig. 10). In order to follow 

 the fibrils which pass downwards from the basal corpuscles it 

 is necessary to remove the chondriocontes, which often prevent 

 close examination. This is realized practically in poorly pre- 

 served portions of the sublimate or Meves materials. Sections 

 from such portions show that the fibrils in question (fig. 11) 

 pass, in a slightly tortuous course, through the cytoplasm towards 

 the distal end of the nucleus. These fibrils (corresponding with 

 what are designated as rootlets of the ciha) appear not to be 

 free, but to be connected with protoplasmic networks and are 

 not to be confounded with the chondriocontes, which seem to 

 be suspended on or embedded in the beams of the network 

 and never pass into the transparent zone. Centrosomes and 

 mitosis of ciliated cells occur not infrequently; two-nucleated 

 cells also often are met with. 



6'. The intestine of Helix. There exist no noteworthy differ- 

 ences in structures of cihated cells between the intestine of Limax 

 and that of Helix, so that its description can be omitted. 



7. The epidermis of Am-phihian larvae. The epidermis of 

 young Amphibian larvae is composed of two layers ; in the upper 

 or cuticular layer, there are two kinds of cells: non-ciliated and 

 ciliated cells. The latter (figs. 27-32) are few in n amber and 



