-j^^ K. MITSUKURI; 



therefore arises within the area covered ventrally by the cells derived 

 from the primitive knob. 



It is necessary to call attention here to the cliange of shape which 

 the blastopore undergoes in the course of the above events. Wood- 

 cut Y gives out- 

 Woodcut V. lines of the blastopore, 

 -j^ ^ 3 as actually observed in 



one series of embryos of 

 Ghclonia caoiuum. As 

 they were successively 

 taken from the same de- 

 posit of eggs at certain 

 intervals of time and 



7 



as the changes of the 

 J ^ shape are corroborated 



Diagrams showing changes of shape in the bhxstopore. ]^y other series of Cm- 

 The figures of entire embryos arc given mostly in Contrib. • i i 



IV. and that of (7) in Fig. 1 of this article. bryos Similarly obtain- 



ed, I think they may 

 be assumed to be correct. In (7), the blastopore is a wide open cavity 

 rather elongated in the transverse direction. In (ß) it is a crescent- 

 ic transverse slit, no longer gaping, with its concavity turned 

 forwards. In (5), it is nearly straight across, in this case with a 

 slio-ht notch in the median line open backwards. In {^) and (5), the 

 ends of the slit-like opening have been turned backwards so tbat the 

 concavity now faces l)ackAvards. In (6), it is a deeper crescent, also 

 with its concavity ficiiig backwards. In ("), it has assumed a deep 

 horse-shoe shape. In i)assing, I ought to mention that I have Ijeen 

 able neither to discover the stage (reproduced in AYoodcut I. A) given 

 by AViLL as occurring at tlie earliest period, ])resumably previously 

 to (i) of Woodcut v., nor to make out [iuy for ward encroachment of 



