221 



between ectoderm and yolk. They appear both between cells of the 

 neighboring part of the ectoderm, and between cells of the neigh- 

 boring part of the yolk. In Fig. 12 which represents a part of the 

 ventral lip and adjoining yolk, drawn at 7,45 P.M.. a number of 

 these dark, angular, minute areas may be seen in the yolk. Dark 

 lines also may often be seen (as in Fig. 12) extending in from the 

 just formed lip, between the yolk cells. The spots and lines so evi- 

 dent at 7,45 P.M. were seen to be gradually covered up by the 

 blastopore lip. The apex of the yolk cell, indicated by the reference 

 line 1 in Fig. 12, was 99 /t from the ventral lip at 7,45 P.M. At 

 8,15 P.M. it was only 55 f.i from the lip; and by 8,40 P.M. the 

 hp had reached the apex (note difference in rate of movement). — 

 The successive views of the blastopore, shown in Fig. 13 (a, b, c). 



Fig. 13. Successive views (a, b, c) of blastopore of same compressed 

 which Fig. 12 was drawn, v. I. ventral lip. 



I, from 



were drawn at 8.45 P.M., 9,25 P.M., and 10 P.M. respectively. In 

 Fig. 13 a the reference line 1 points to the apex of a cell, 198 /< 

 from the ventral lip at 8,45 P.M. In 30 mins. the lip moved 44 /t 

 nearer this apex. In Fig. 13 b (9,25 P.M.), the reference line 1 

 points to the apex of a cell 66 n from the ventral lip ; at 9,40 P.M. 

 the apex is only 44 /< from the lip ; and at 10 P.M., it is only 22 f.t 

 from the lip. — A natural mark is shown at x in Fig. 13 a (8,45 P.M.). 

 It was a peculiar depression, darker in color than the surrounding 

 area, and continued to be recognizable until shortly after 10 P.M. 

 This depression at 8,45 P.M. was ueai-ly equidistant from the ven- 

 tral and dorsal lips — slightly nearer the former. From 8,45 P.M. 

 to 10 P.M., the blastopore changed shape, and diminished con- 

 siderably in size, its dorso-ventral diameter decreasing from 51 micro- 

 meter divisions to 35 such divisions (value of each division, 22 /n). 

 During this contraction of the blastopore however, the depression 

 preserved its relative position with respect to the ventral and dorsal 



