234 EIOHARD ASSHETON. 



lip of the blastopore had gained a little upon the mark. After 

 a lapse of eight more hours tlie blastopore was very much 

 smaller, and the mark was found partly covered by the dorsal 

 lip. In this (fig. Id) the ventral lip had gained much more 

 upon the mark than had the dorsal lip. 



Figs. 2« — 2d are figures of a specimen which had a natural 

 mark upon the white pole of the ovum. The drawings were 

 made at 5.30, 8.30, 10.40 p.m., and 8.30 a.m. 



I thought the scar was part of the embryo, but upon the 

 blastoporic rim reaching it the scar became partly scraped off 

 on to the rim. 



Both this specimen and the last show that the apparent over- 

 growth of the dorsal lip of the blastopore is much more marked 

 at first than afterwards. 



This is well illustrated by figs. 4«, 46. In this specimen 

 a mark was made after the complete formation of the blasto- 

 pore (fig. 4a) near the centre of the unenclosed yolk. Fig. 

 46 is the same specimen seventeen hours afterwards. I do not 

 know to which lip the mark was approximated. 



Figs. 3 a — Sg show a similar apparent overgrowth of the 

 dorsal lip, and also that this overgrowth is greater during the 

 earlier period of blastopore formation. 



Figs. 5 b, 5 c, and 5d are from embryos which have completed 

 the closure of the neural plate. All these were, at the moment 

 of the first signs of the blastoporic lip, pricked near to the 

 margin between the black and white at the point most distant 

 from the commencing blastopore, and equidistant with the 

 latter from the equator of the ovum. Fig. 5d shows the scar 

 a little to the left of the spot where the blastopore has closed. 



Fig. 56 shows the scar upon the side of the embryo about 

 its middle, both dorso-ventrally and antero-posteriorly. 



Fig. 5 c shows the scar upon the ventral edge of an unclosed 

 blastopore. In this specimen the injury was very severe, a 

 large mass (exo.) exuded, and, as always follows in such a 

 case, an abnormal embryo was formed. 



Fig. 5 a shows the spot near which they were all pricked. 



Ten embryos were pricked in the centre of the lower pole of 



