ON THE FORMATION OF THE GERMINAI- LAYERS IN PETROMYZON. 



Explanation of Figures. 



Complete list of reference letters. 



(HI. V. iinditorv vesicle. 



/;/). l)]astopore. 



cli. cliovda. 



ch. h. chorda-livpoblast. 



e2>. epiblast. 



en I. enteric cavity. 



hb. liiiid brain. 



hch. hypochordal celJy. 



Iqy. hypoblast. 



it. invaginated tul»'. 



//). lateral plate (of mesoblast). 



mes. irie.soblast. 



uies.y. iiiesoblastic told. 



mes. /). peristomal mesoblast. 



mes. f>. mesoblast Ic somite. 



II. neural cord. 



iif). neural or medullary plate. 



J). J), e. pleuro-peritoneal cavity. 



/'. iiie.s. parietal mesoblast. 



/•. mes. visceral mesoblast. 



s. segmentation cavity. 



vti. somatic mesoblast. 



i/f. yolk-ci'IIs. 



145 



