GEOWTH IN LENGTH OF THE PEOG EMBRYO. 235 



the ovum in the blastula stage before any trace of the dorsal 

 blastoporic lip could be detected. Of these when preserved, at 

 which time the normal ones were from 4| mm. to 5 mm. in 

 length, seven showed no trace of the injury externally, and 

 seemed to be quite normal. One showed no injury, but was 

 rather abnormal in shape. Two failed to develop beyond the 

 blastula stage. 



Another specimen was pricked, as shown in fig. 6a, on both 

 sides of the blastopore, on one side upon the lip, on the other 

 a slight distance away from the line where the lip was appa- 

 rently about to develop. Fig. 6b was drawn ten and a half 

 hours afterwards. 



After the blastopore had closed I was unable to detect the 

 injuries. 



There is no doubt that one must be very cautious indeed in 

 drawing conclusions from injuries made upon eggs. This is 

 especially so with injuries made upon the more active part of 

 the embryo, i.e. the more deeply pigmented cells. A verv in- 

 considerable injury is sufficient to produce an abnormality. 

 Three slightest punctures possible upon the rim of the blasto- 

 pore equidistant from each other are sufficient to prevent the 

 closure of the blastopore, while one only, if at all severe, will 

 have the same effect. 



This clearly must be the case, as the closure of the blasto- 

 pore is an eflFect of increase of bulk of certain parts of the 

 walls of the embryo, and if this increase in bulk is, through 

 pricking these walls, prevented or delayed by the letting out 

 of matter, and thereby obviating the necessity for the blasto- 

 poric lip to advance, the blastopore does not close; and so also 

 injuries to the white pole or yolk plug by allowing the escape 

 of material from that area, and thereby diminishing the bulk 

 of the part of the embryo that can be covered by the advancing 

 lips of the blastopore, hastens the closing of the blastopore. 



My own experiments are in part confirmatory, but mostly 

 contradictory to those of E.oux, They are upon the whole 

 confirmatory of those performed by Morgan and Ume Tsuda. 

 Roux asserts that the dorsal lip of the blastopore passes pver 



