40 EMBRYOLOGY OF THE LOWER VERTEBRATES CH. 



accompanied, no doubt, by a certain amount of involution though 

 this is difficult to determine with certainty, has proceeded much 



ent 



J-'i'.. 25. Sagittal sections through the egg of llmm tem/Hn'nrin illustrating tin- ]>r< 

 trulation. (After Jenkinson, 1913.) 



ect, ectod'-nii; tnt, .nrli.-jili-i i<- <-a\ity; ;/./, ^astnilar lip; *.<; Kf^inentjition cavity; ;/./>. yulk-iilug. 

 'J')n- arrow indicates the original apical pnlr. 



liirther so that the archenteron is much deeper. The spreading of 



tin- yolk-cells ;ili>u;j tin- rnol' of (he sr^nnMit.-i 1 im ravity. alrcadv 



