PLATE 2 



EXPLANATION OF FIGURES 



5 Right half of complete filament. A binulceated cell of the lateral epithe- 

 lium (L), differentiated from the non-ciliated cells of the basal epithelium, is 

 still almost in a basal position. Amitotic nuclear division has occurred in the 

 cell {N), in the laterofrontal position, with the pairing of the cilia and the basal 

 granules. A degenerating cell (D) of the frontal epithelium, with a pyknotic 

 nucleus surrounded by a vacuole, is situated toward the interior of the filament. 

 The cells of the frontal epithelium (.4) have short worn-off cilia and vesicular 

 nuclei. The mitochondria, predominantly of bacillary and filar form, are aggre- 

 gated in the distal border of the cells. 



6 Transverse section of half of a filament. The primitive cell of the lateral 

 epithelium has suffered amitotic division, forming transitional cells (T). Each 

 daughter cell is of the tall columnar variety and shows in vertical sections a pair 

 of cilia and a pair of basal bodies. A remnant (M) of the primitive cell (M and T) 

 is undergoing belated nuclear division. The pairing of the basal granules and 

 the cilia is conspicuous next the uppermost of the group of daughter cells (T). 

 Two of the frontal cells (C) are in stages of degeneration. 



7 Transverse section of gill filament, showing frontal epithelium (A), mul- 

 tiple direct nuclear division with pairing of cilia and basal bodies in the latero- 

 frontal epithelium (//), and the lateral epithelium of one side composed of two 

 cells (L). 



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