PIECES OF FROG EMBRYOS CULTIVATED IN LYMPH. 2O5 



in addition to several larger lobes, a number of finger-like proc- 

 esses which very closely resembled the filaments of the gills. 

 The central part of these projections was composed of connective 

 tissue, and the epithelial covering consisted of a layer of columnar 



FIG. i. Piece from the head of a frog embryo drawn fifteen days after being cul- 

 tivated in lymph, e, isolated ectoderm cells. 



ciliated cells. These outgrowths began three days after the 

 preparation was made, and they were practically completely 

 formed in a week. Fifteen days after the piece was mounted it 

 had assumed the form shown in Fig. I. The cilia on the projec- 

 tions were beating, and in fact they continued active for two more 

 weeks, but there was little further change in the general form of 

 the piece. When originally mounted the piece was opaque, 

 and the cells composing it contained a large amount of yolk. 

 After two weeks it had become nearly transparent; the larger 

 part of the yolk in the cells had been assimilated, and a typical 

 connective tissue had developed in the interior from the com- 

 paratively unspecialized cells of the mesoderm. The piece was 

 covered completely by ectoderm which, over most of the surface, 

 was flattened, but assumed a cylindrical form on the more promi- 

 nent projections. In the third week a layer of epithelium was 

 sloughed off from a large part of the surface of the piece. 



Whether the finger-like processes represent gill filaments is 

 more or less open to question. Processes of this kind failed to 

 make their appearance from the hinder part of the embryos. 



