392 T. H. MORGAN AND Um6 TSUDA. 



anterior, lateral, and posterior edge of the blastopore points to 

 the same conclusion. 



I believe, however, that the details of the actual process of 

 concrescence of the blastopore has not as yet been accu- 

 rately worked out. The migration of cells that takes place 

 during the process has not been determined. Whether or not 

 the dorsal lip rolls in as it grows over, or whether its ex- 

 posed edge always carries the same cells, has not been shown. 

 Both experimental and structural evidence must be brought to 

 bear on the problem before its solution will be possible. 



A series of ten experiments were made by sticking the 

 embryo (when the blastopore first appeared) at the apex of the 

 black pole. Other experiments involved sticking at the apex 

 of the black and white in the same egg. The latter experi- 

 ment ought to settle the question as to what portion was the 

 active agent in the overgrowth. Unfortunately the experi- 

 ments did not give satisfactory results, nor were the results 

 uniform. Injury to the delicate roof of the segmentation 

 cavity may have helped to produce poor results. Failure to 

 find in the later stage the point injured, shifting of the extra- 

 ovate if large, and the difficulty of determining the exact 

 apex, may all have had a hand in the matter. Only two such 

 embryos are drawn, although other as definite records were 

 also obtained. 



Experiment VII (fig. 5). — Egg when blastopore had just 

 appeared was stuck at apex of black pole. When the medul- 

 lary folds appeared the injury was found on the ventral surface 

 of the body, as shown by the x in the figure. The defect was 

 at about equal distances from the anterior end of the medullary 

 folds and from the blastopore. 



Experiment VIII (fig. 6). — Injured as in last. Defect 

 appeared at point 180° from blastopore, therefore some distance 

 in front of the anterior end of the medullary folds. 



Both of these results show that the embryo does not form 

 over the black pole, but why in these cases the defects are 

 at such diff'erent distances from the blastopore I do not 

 know. 



