FATE OF BLASTOPORE, ETC., IX CHELONIA. gj 



k is seven sections beliind ;". The mass witliin the tail 

 shows some sliirht trace of tlie mediillarv chord in its 

 upper dorsal part. The ]»rimitive streak is still persistent, 

 althoui^h it is not as distinct as in front. This is the 

 last section in Avhich the primitive streak is visil^le. 



I is next to h. The tail now consists only of the indifferent 

 cell -mass surrounded by the epiblast on the outside. 



There are five sections behind / in which the tail is 

 visible, alth<jugh gradually reduced in circumference. 



In the fourth sectitjn behind / there is a structure standing up 

 from the iioov of the postérieur amniotic tulje which is figured in Series 

 XIII m (PI. X.). Tliis is so similar in appearance and position to the 

 yolk- plug observed in earlier stages that we must conclude that here we 

 observe its remnants. This is found in six sections, in threß of which 

 it is quite prominent. The one figured is the second of the three 

 prominent sections and the second of the six. This is the last stage 

 in which I was able to detect the yolk-plug in sections. 



Of the primitive streak which was [)resent in earlier stage (Series 

 IX and Woodcut VII), only a small portion in the ventral median line 



in the anterior part of tlie tail remains 

 Woodcut IX. at this staue. The formation of the 



,,- -ii;r- --- ^'^i^ ^jy iipheaval easily explains the 



.^;'.v \\ presence of a part (jf the primitive streak 



/' ;'-' in the ventral median line. If Wood- 



^^''' cut \il (|t. ô()) re[)resents the extent 



;'; of the primitive streak at the staire of 



\\ 



Series IX, we may consider Woodcut 



IX as re[)resenting (lie state ()f things 



in tlu' [»resent series. The dotted part 



has disappeared and only the j)art given in the full hue, together with 



the yolk-plug, now reniaii)s. The proctoduMun seems to Ije formed 



