288 S. J. HOLMES 



yolk in the form of tiny spherules may persist until a late larval 

 stage, even in the ectoderm of the tail and dorsal side of the body, 

 while it is fairly abundant in the cells of the ventral side of the 

 abdomen. As the cells become older and the yolk is gradually 

 used up they tend to become relatively broad and thin, and to 

 increase in transparency. Certain cells in early larval develop- 

 ment become distinctly alveolar in structure (fig. 5) . Such cells 

 occur either singly or in small groups scattered about among 

 the cells with homogeneous protoplasm. The alveoli are of 

 various sizes in the same cell. These cells resemble and prob- 

 ably correspond to the Leydig's cells which have been described 

 from the epidermis of several amphibians. I have observed 

 the same type of cells scattered about in the epidermis of the 

 young larvae of Diemyctylus in much the same way as they 

 commonly appear in epithelial extensions in vitro. In the 

 young larvae of Triton, Salamandra and Siredon, Maurer^ de- 

 scribes the Leydig's cells as scattered about singly among other 

 cells of the deeper epidermis. On account of their vacuolated 

 protoplasm these cells are considered as glandular in function, 

 but they take no part in the formation of the cutaneous glands 

 of later development. It is the appearance of the alveolar con- 

 tents of the Leydig's cells that has given rise to the common 

 opinion that they are mucous glands, but the cells have no direct 

 connection with the exterior, and are usually covered with one or 

 more layers of ordinary epithelium. In the preparations of 

 epithelium in vitro various intergradations were found between 

 ordinary epithelial cells and cells of the vacuolated type. 



Occasionally also cells with granular contents occur in the 

 epithelial outgrowths (fig. 4). The material forming the granules 

 has a different appearance from the yolk, and probably repre- 

 sents the accumulated product of some sort of secretion. 



As we have mentioned before, preparations may be kept alive 

 for a considerable period if they are changed to a fresh culture 

 medium. No especial attempt was made to find how long tissues 

 could be maintained alive, but some of my preparations of epi- 

 thelium were living over three months after implantation. One 



•'' Maurer, F. Die Epidermis uiul ihre Abkoininlinge. 



