AMITOSIS IN CILIATED CELLS 107 



pyknotic (figs. 5, D, 6, C) and finally disintegrates by karyor- 

 rhexis. Such necrotic material is resorbed basally, and new 

 cells are pushed over and into place of the degenerated ones. 



In the ciliated epithelium of the alimentary tract of Cyclas 

 I find that cellular proliferation takes place by mitosis (fig. 2). 

 The epithelium of this region is of the tall columnar variety. 

 The nuclei of these cells are situated proximally and are pale 

 staining. Each cell has a tuft of moderately long cilia extending 

 from its distal border (fig. 2). The cilia are attached to a 

 double row of basal granules, and from the innermost row of 

 granules a cone of rootlets extends down into the cytoplasm, 

 the apex of the cone falling on one side of the nucleus. The 

 cytoplasm of these cells contains some filar and bacillary mito- 

 chondria. Centrosomes could not be detected in the cells with 

 cilia. Mitosis in these cells takes place only before cilia have 

 appeared, or after they have disappeared. 



REVIEW OF LITERATURE 



In 1877 Peck^ published a description of the lamellibranch 

 gill, which has formed the basis for all subsequent text book 

 accounts. In this comparative investigation Peck devoted 

 special attention to the histologic details of the gill epithelium in 

 Anodonta. He distinguishes in this form "frontal, latero-frontal, 

 and lateral epithelium." He described all cells as being ciliated. 

 "Those of the latero-frontal rows (a single row on each side of 

 the frontal epithelium) have the longest cilia, far outreaching 

 those of the other cells; the frontal epithelium and the more 

 forward cells of the lateral epithelium come next with finer and 

 much shorter cilia, and lastly, the inlying lateral epithelium has 

 but very short cilia." He calls especial attention to the cells 

 of the laterofrontal epithelium, and describes these cells as being 

 larger than their neighboring cells, and appearing from the 

 surface like goblet cells with a single coarse flagellum issuing 

 from them, while if seen in a transverse section of a filament 

 these cells appear broad and a little flattened, the single flagellum 

 proving to be an adhering group of long cilia. The nucleus of 

 these cells he described as large and clear, and as enveloped by 



