EPIDERMIS WHEN CULTIVATED OUTSIDE BODY 289 



cross section taken from the tail of a young Diemyctylus larva 

 before it hatched from the jelly was put up in the middle of 

 January. In a few days the epithelium showed extensive out- 

 growths along the cover slip and lower surface of the hanging 

 drop. On January 27 after it had begun to show signs of de- 

 terioration it was washed and transferred to fresh gelatin and 

 serum. Growth was resumed, and the cells showed a healthy 

 appearance. The piece was transferred to fresh medium on 

 February 2, and again on February 18. On February 24 it was 

 divided into two parts. Both pieces, although their epithelial 

 extensions became much shrivelled up after the transfer into 

 fresh culture medium, soon put out extensive sheets of epithelium. 

 Both pieces were transferred on March 3, when the same con- 

 traction and subsequent extension were again observed. One 

 piece was transferred once more on March 10, and hved about 

 a month longer. It is represented in figure 10. The second 

 piece which showed signs of diminished vitality in the rounding 

 up and separation of many cells and cell masses was re-transferred 

 on April 1, after which it became active and sent out extensive 

 sheets of epithelial cells. 



The histories of many other preparations were essentially the 

 same as the foregoing. In all cases the tissue was washed in 

 Ringer's solution for a half hour or more, and the old gelatin 

 mass around it removed before being put into a new supply of 

 nutrient medium. A few preparations were left in Ringer's 

 solution for a day without any apparent harmful results. 



Epithelium remained epithelium throughout the experiments. 

 The changes occurring in it were comparable to those taking 

 place in the epithelium on the body of the larva. There was a 

 progressive loss of yolk spherules, which in the epithelium from 

 the dorsal side of the larva resulted in the total disappearance 

 of yolk from most of the cells. As the yolk disappeared the cells 

 became thinner and more expanded. From cells originally alike 

 in appearance there came to be differentiation into cells of the 

 vacuolated type, granular cells, although the latter were com- 

 paratively rare, ciliated cells, and cells of typical pavement epi- 

 thelium. Whether the cells had received a start toward diiTer- 



