394 AN INTRODUCTION TO ZOOLOGY 



but are represented by a number of scattered somewhat stellate 



I 



M 



FB 



FIG. 135. -Rana temporaries. Diagrammatic sections of sagittal sections of 

 young embryos: I., before closure of blastopore ; II., after closure of 

 blastopore. 



A., anus ; B., blastopore ; E., ectoderm ; En., entoderm ; F.B., fore brain ; F.G., fore gut ; 

 H., heart rudiment ; H.B., hind brain ; H.G., hind gut : L., beginning of liver diverticulum ; 

 M., mesoderm ; M.B., mid brain ; M.G., mid gut ; N., notochord ; N.E., neurenteric canal ; 

 O., oral evagination ; P., pituitary ingrowth ; Pi., pineal outgrowth ; Pr., proctodosum ; R., 

 rectum ; S.C., spinal cord ; Y., yolk cells. 



cells filling in the interstices between the brain and ectoderm and 

 front end of the enteron. Mesoderm in this condition is frequently 



