11 



apart jr zuch a -r.rner an to forin a curvec sheet. In others 

 this separaticr ard virrcllirp: of the hlastomeres was lers 

 defiritehr'd the final arrangement v/ac such as shorn ir Fip- 

 ure IC. 



The irreriilarity ir the relative "ositior of the blasto- 

 rereslberins rith the eight cel'rd stare ard is r-rre or less 

 charaeteristic of all later stages ur to the f creation of 

 the blastula. But, while there is diversity of arrargerent 

 of the bi astc-eres , reverthrless I ar led tc believe 

 that the civisior of the individual cells is regular and 

 takes .iust ar though the blastcreres alv;ays held the same 



A 



relative nosition. 



The fourth. segTentation foHcvs after a short ner^od 

 of tine. Figure li Ehov;s a sixteen-celled stage v-hich is 

 nearly regulrr, but the cleavage cavity has already been form- 

 ed v,'lthin the rassjof blastcreres a-d they are thus nushed 

 av/ay fror the centre of the epp. In this stage the cell 

 lineage can still be traced even i^ the forrrs that are scre- 

 v-hat irregular. But in -.hejblder stages the arrange-^ent of 



