54 Primitive Streak and Notochordal Canal in Chelonia. 



EXPLANATION OF PLATES. 



All figures on Plates I.-III. were outlined by means of a camera lucida, and shaded 



free hand. 



ABBREVIATIONS. 



a Individual a of a pair of twins. 



/3 . > Individual /3 of a pair of twins. 



bPpo. a Anterior lip of the blastopore. 



trpo. p Posterior lip of the blastopore. 



can. tCent. . . ^ . . Neurenteric canal. 



' can. nfcd. Notochordal canal. 



cl. vt Yolk cells. 



ec'drm Ectoderm. 



ec^en Ectental line. 



en^drm Entoderm. 



en^drm. a Entoderm of embryo a. 



en'drm. d. ^ . . . . Dorsal entoderm of embryo p. 



en'drm. w. /3 . . . . Ventral entoderm of embryo j3. 



so'plu Somatopleure. 



sir. pr. Primitive streak. 



sul. pr Primitive groove. 



sul. pr. a Primitive groove anterior to the neurenteric 



canal. 



sul. pr. p Primitive groove posterior to the neurenteric 



canal. 



