Early Development of Desmognatlius Fusca. 543 



for Amphibia ; it seems to slightly resemble conditions which result 

 in the development of certain stages of fish eggs. 



External features of blastopore formation seem to be not unlike 

 the similar stages of other Urodela; a minute depression marks the 

 beginning of gastrulation, later a half ring-like groove, Fig. 28, and 

 still later a complete ring-like blastopore comes to be fonned (Fig. 

 29). At a still later stage only a little dimple is seen from the sur- 

 face of the egg and a small mass of yolk projecting from the small 

 opening represents a typical yolk-plug stage. ISTo indication could 

 be obtained from the exterior of the exact place where gastrulation 

 began. Sections of a number of eggs during early gastrulation show 

 various stages of ingrowth of small cells on the surface into the solid 

 mass of yolk-cells which make up the greatest bulk of the egg. This 

 ingrowth which may be recognized in sections of stages similar to 

 Figs. 28 and 29, seem to start in about the central part of the area 

 covered by small cells and seems to concern itself wdth the small 

 granuled surface cells. These cells seem to multiply and push them- 

 selves down into the larger yolk-cells forming a more or less sharp 

 cleft between them, Figs. 54 and 55. Whether this down growth 

 is entirely confined to the multiplication of surface cells, or 

 whether the adjoining yolk-cells contribute to some extent, it is difii- 

 cult to determine from the evidence which is at hand at present. I 

 can only say that this cleft in the cells seems to be chiefly due to the 

 growth of the surface cells down into the mass of other larger cells 

 which have larger yolk granules. 



In a section of a later stage, such as given in Fig. 58, a small 

 yolk-plug is shown. There has come about a rearrangement of cells 

 in such a way that we can recognize clearly two layers of small cells 

 on the dorsal lip of the blastopore and a thickened mass of the ven- 

 tral lip. A yolk-plug of not very clearly defined, large granuled yolk 

 cells projects between the two lips and this mass of yolk for some 

 reason, seems different from the more definite cells which occupy 

 the larger part of the egg. These last cells seem to be little 

 changed from what they were in slightly earlier stages. The region 

 occupied by the less easily defined cells, the mass of which projects 

 from the mouth of tlu; blastopore as yolk-plug, is well separated from 



