420 J. (ilJAHAM KEKJv'. 



as ordinar}' cells of the epidermis, whose c_vto])lasin assumes 

 a clear vacuolated appearance, the whole cell remniiiino- in 

 form and size like its neighbours. By Stage 38 the gland- 

 cells have become predominant by their size, and they are 

 also elongating in shape. 



The multicellular glands appear about the same time as 

 downgrowths of the deep layer of the epidermis, and here 

 again we find that the rudiment is solid, and the cavity 

 appears secondarily. This we can naturally not put down, 

 as we do in the case of certain other organs arising similarly, 

 to any such simple cause as the presence of yolk. By Stage 38 

 a large cavity has appeared, but it is not yet open to the 

 exterior. 



Cement Organ. 



A remarkable local development of epidermal gland-cells 

 is afforded by the cement organ, which, as indicated before, 

 retains through life the crescentic shape shown by Thiele to 

 be characteristic of the organ in its early stages in Batra- 

 chians. It is a curious point, however, to which my attention 

 was first drawn by my friend Mr. Bles, that in the Amphibia 

 the organ is derived from the superficial layer of the epi- 

 dermis, not the deep layer as in Lepidosiren. 



The first indication of the cement organ appears about 

 Stage 23 (PI. 25, fig. 3 a) as a slight thickening of the deep 

 layer of the epidermis, the superficial layer passing over it 

 hardly affected. By Stage 25 the thickening has considerably 

 increased, and the superficial layer now shows signs of break- 

 ing down over the middle of the gland, so that here the deep 

 cells are exposed to the external medium (fig. 3 b). By 

 Stage 31 the gland is fully functional. Its cells are tall and 

 columnar with nucleus at the base, and protoplasm showing 

 peripherally a clear transparent appearance. 



During the later stages of development tlic glandular 

 surface becomes involuted slightly, and at the same time its 

 lower edge becomes tilted up somewhat, so that the organ 

 projects conspicuously above the adjoining skin surface. 



