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Chas. B. Wilson 



starts as »an irregular broken line lying just below the equator and 

 formed by the union of a number of cleavage furrows «. In the 

 present instance this line is even more irregular and angular, and 

 it begins much nearer the vegetative pole (Figs. 1 and 2). It bears 

 the same relation to the more deeply pigmented area of the superior 

 hemisphere as in normal development and as noted by Tsuda (39), 

 in Eana temporaria, i. e., it starts just beneath it. The pigmented 

 cells, however, as can be seen from Fig. 1 , which represents a camera 

 lucida drawing of the surface of a living egg, stop at some little 

 distance from the edge of the blastopore, and the latter is wholly 

 surrounded by large yolk cells which are entirely free from pigment. 

 Moreover these are the largest of the yolk cells, and should be, 

 therefore, those formed at or near the vegetative pole. Clarke (8) 

 states that invagination normally begins at the vegetative pole in 

 Amblystoma, while F. Houssay finds the same true for the Axolotl 

 (26), Jordan for the Newt (29), and Tsuda for Rana temporaria (39). 

 The present experiments Avould seem to yield good testimony in the 

 same direction. 



At first the gastrula groove is much branched and follows almost 

 exactly the boundary lines between some of these large yolk cells. 

 But it becomes more even later on and turns upward, eventually 

 running around the egg about one third the distance from the vege- 

 tative pole. This may be seen in Fig. 2, another surface view of a 

 living egg farther developed. Here the furrow is crescentic and 

 comparatively regular, but at first the convex side of the crescent, 

 instead of the concave side, is turned toward the yolk field. I fully 

 agree with Morgan that the yolk exposed is somewhat more than 

 would be enclosed by the normal blastopore, and that »any state- 

 ment as to the extent of white closed over by normal embryos, 

 based on these abnormal embryos, will give an erroneous con- 

 clusion « (39). 



Formation of the Pigment. 

 The pigment is formed in situ in the yolk cells themselves, 

 and can be seen as minute dark spots upon their surface. It certainly 

 cannot be regarded as in any way of ectodermal origin for no ecto- 

 derm is formed over the yolk plug. But it does seem to be intimately 

 associated with the centers of physiological activity as Jordan 

 suggests. 



In normal development it does not usually appear among the 



