TO THE EMBRYOLOGY OF AMPHIBIA. 



43 



closed, the yolk-plug having already been withdrawn into the 

 interior. The first trace of the neural groove may be recognized 

 along the median line of the neural plate which is now raised 

 somewhat over the general surface of the egg. 



Figs. 60 and 61 give the corresponding sections of the stage 

 represented in Fig. 15 or in Fig. 38. The blastopore is completely 

 closed, and the neural groove is nearly so, so that the general 

 outline of the embryo-body can now be distinctly made out. 



In the above series of figures, the horizontal line drawn under 

 each gives the surface on which the egg was resting at a given stage, 

 and the lines drawn parallel and vertical to this show the hori- 

 zontal and vertical axes of the egg as it then stood. The dotted 

 line in Figs. 55, 57, 58, and 60 shows, on the contrary, the ideal 

 vertical axis or the line which passed through the upper and 

 lower poles of the egg at the blastula stage, and which shifts 

 its position through the gradual rotation of the egg around its 

 transverse horizontal axis. If the egg were supposed to be held 

 to its initial vertical axis without any rotation, the series would 

 become as in Woodcuts I-IV. The two dotted lines at right 



Seg.Cav.iv~ 



The thick line in front of the blastopore indicates the extension of the neural plate. 

 Seg. cav. 1 , Seg. cav. 11 , Seg. cav. lir , Seg. cav. IV , the gradually diminishing seg. cavity. Arch. 1 , 

 Arch. 11 , Arch. 111 , Arch. IV , the gradually enlarging archenteron. 



