AMITOSIS IN CILIATED CELLS 105 



b. Lateral epithelium.. Here the cells are for the most part 

 ciliated. The lateral epithelium of a gill filament at any point 

 may be composed, on one or both sides, of a single row of tall 

 cuboidal cells (fig. 4, L) or of several rows of columnar cells 

 (fig. 7, L). (The illustrations are of transverse sections of the 

 gill filaments. In longitudinal sections of the filament the 

 several types of cells occur in long rows.) 



The cilia of these lateral cells are long and heavy, and are 

 attached to a single row of basal granules lying under the striated 

 border (fig. 1, L, 4, L, 5, L, 7, L). The nuclei are vesicular in 

 character. Amitosis can occasionally be seen in these cells 

 (figs. 1, 1/, 4, L, 5, L, 7, L). This process begins with the inden- 

 tation of the nuclear membrane (fig. 4, L), which indentation 

 deepens until two nuclei are formed (figs. 1, L, and 5, L). The 

 nuclei separate, after which there follows a cytoplasmic division 

 (fig. 7, L). The cytoplasm stains only lightly and contains 

 filar and bacillary mitochondria, most of which are distal 

 to the nucleus. No centrosome can be detected in a single in- 

 stance. Between these cells and the later of rontal epithelium 

 several small non-ciliated cells may (fig. 1, /) or may not (fig. 4) 

 be interposed. 



c. Laterofrontal epithelium. The laterofrontal epithelium is 

 derived from the lateral cells and replaces the worn-out cells of 

 the frontal region. The parent cell or cells of this region comply 

 with the same description as the cells of the lateral epithelium; 

 they are in fact identical with these cells, but in a different posi- 

 tion. The nuclei, however, soon enlarge and become hyper- 

 chromatic (fig. 1, P). The first indication of nuclear division 

 is the indentation of the nuclear membrane (fig. 4, N). The 

 nucleus undergoes a multiple division, and from one nucleus, 

 by amitosis, a number of daughter nuclei are formed (figs. 5, 

 A^, 7, H). Coincident with nuclear division th«^re occurs a dis- 

 tinct pairing of the cilia and basal bodies (fig. 5, N, 7, H). Cyto- 

 plasmic division follows, and thus is formed a new type of cell, a 

 columnar cell with a deeply staining, narrow, elongated nucleus 

 (fig. 6, T). The cytoplasm contains filamentous and bacillary 

 mitochondria. Each cell possesses four paired flagella-like cilia 



