60 THE AMPH1OXUS. 



The absorbed moisture of the segmentation cavity 

 may indeed have partly contained the albuminous 

 substances separated from the segmentation cells, and 

 which were now again taken up by the hypoblast 

 cells. To a great extent this moisture was diluted 

 indeed with sea water which evidently fills up that 

 space within the vitelline membrane with which the 

 segmentation cavity in the early stages (up to the stage 

 with sixteen cells, Fig. 9) was in open communica- 

 tion. 



On a closer examination of the flat gastrula stage 

 (Fig. 24) the bilateral symmetry can already be dis- 

 tinguished, that is to say, the right and left side of the 

 body, while in the blastula only a chief axis was dis- 

 tinguishable. 



This may quite well be recognised in profile in the 

 irregularity of the curvature (Fig. 24), as also, on 

 examination of the embryo from the gastrula-mouth, 

 the outline here appearing not circular but somewhat 

 oval (Fig. 25). 



Fig. 24 is not, like the former ones, constructed 

 with reference to the axis from the upper to the lower 

 pole, but, like the succeeding figures, according to the 

 later longitudinal axis. It is now time to mention 



