1883.] 207 [Jeffries. 



and mucleoli are like those of the mucous cells. The cells of 

 this layer seem to undergo division, though dividing cells have 

 not been noted. My reasons for supposing this are, first, that 

 at a later period of growth the cells form a compact layer; 

 second, that two nucleoli are present. 



By the middle of the sixth day, though in places the epiderm 

 is the same as before, a decided change has occurred. Cells have 

 already begun to divide off from the mucous layer and to form 

 a more or less continuous layer between the mucous cells and 

 those of the epitrichial layer. In nature and dimensions of parts 

 they are very much like those of the mucous layer, but differ in 

 that, as a rule, only one nucleolus is to be seen. I have not ac- 

 tually traced the formation of these cells, but judging from sec- 

 tions (fig. 3) it would seem that they are simply divided off 

 from the ends of the mucous cells. At all events, in the places 

 where no cells intervene between the mucous and epitrichial 

 cells the former are columnar and provided with rather long 

 nuclei with a nucleolus at each end. On the other hand, where 

 cells do come between the two primary layers the mucous cells 

 are cuboidal and provided with a roundish nucleus and a single 

 nucleolus. 



From the sixth day on cells are slowly divided off from the 

 mucous layer. These, when first formed, closely resemble the 

 mother layer, but gradually undergo changes which tend to the 

 formation of the adult skin. By the fourteenth day but slight 

 advance has been made. The epitrichial cells are still very irreg- 

 ular in shape (fig. 4) and show large patches of intercellular 

 substance between them. 



By the twentieth day the epitrichial layer (fig. 10) has assumed 

 its final form which is the same over the entire body. It now 

 consists of a continuous layer of flat polygonal cells, with broad 

 divisions between them, of about .015 mm. in width and 

 one-fourth to one-fifth that thickness. The protoplasm of the 

 cells is aggregated in little patches or spots, in fact it looks as 

 if it had curdled, while the nuclei and nucleoli are quite indis- 

 tinct. When fully developed the epitrichial cells are not easily 

 stained with carmine or hematoxyline, but become a dark purple 

 when treated with the mixture of eosin and analine blue before 

 mentioned. Thus showing that the activity of the cell is much 



