104 FRANK HELVESTINE, JR. 



In my investigation the chief interest centers about the ques- 

 tions: 1, whether ciUated cells in invertebrates divide only by 

 mitosis; 2, the significance of amitosis in ciliated cells; 3, the 

 relation of the basal granules to the centrosome, and, 4, the 

 relation of the basal granules to mitochondria. 



The material I have employed in this investigation is the cili- 

 ated epithelium of the gill filaments of the fresh-water mussel, 

 Cyclas. I find that in this invertebrate the ciliated cells divide 

 by amitosis exclusively, and no direct relation between mito- 

 chondria and cihogenesis is discernible. 



MATERIAL AND METHODS 



The material for this study was suggested to me by Prof. 

 William A. Kepner. The mussels were shelled and then fixed 

 in various solutions, of which Meves' was found to be by far the 

 most satisfactory. Paraffin sections were cut at 5ij,, and, after 

 mounting, were stained with Heidenhain's iron-hematoxyhn. 

 This technic gave results little short of perfect. 



DESCRIPTION 



For a histologic description of the epithelium of the gill fila- 

 ments of Cyclas, I shall divide the epithelium into four regions 

 according to its position. I distinguish: a, basal epithelium, 

 or the epithelium lying at the base and between adjacent fila- 

 ments; h, lateral epithelium; c, laterofrontal epithelium; and, d, 

 frontal epithelium. 



a. Basal epithelium. The epithelium of this region is non- 

 ciliated (fig. 1, A). The cells on account of their position are 

 more or less pyramidal. They contain one or two vesicular 

 nuclei. Among these cells mitotic figures are occasionally 

 seen (fig. 3, M). The cytoplasm contains many filar and bacil- 

 lary mitochondria collected for the most part toward the periph- 

 ery of the cells. From the cells of this region which he adja- 

 cent to the gill filaments, ciliated cells are formed which are 

 pushed up onto the filament, giving rise to the lateral epithelium 

 (fig. 5, L). 



