14 



K. MITSUKURI. 



distinct. The oldest stage in whif^h I detected any portion of the 

 distal half of the posterior amniotic tube i>; that ^iven in Fig. 67 (PI. 

 VITL). I found there the horse-shoe shaped distal eîid of the tube and 

 the portion contignoiis to it, hnt after n most cnrefnl sf^arch. I could 

 not connect it with fhe proximal part. From tliese facts, it appears 

 that the largest part of the posterior amniotic tidie disappears entirely, 

 and that oidy the proximal |»art — the ])art nearest the amnion proper 

 (prox pt. Figs. 9, 10, and 15, PI. II.) — remains permanently. It will 

 he remembered that the scro-amniotic connection extends from over 

 the neck regi(^n of the embryo to the tip of the |)osterior tube. As 

 the proximal part of the tidoe remains permanently this marks in all 

 later stages the posterior end of the sero-amniotic connection. As fur- 

 ther growth in size of the amnion proper (accommodating itself to the 

 growth of the embryo within it) takes place mostly behind the rem- 

 nant of the posterior tube, the latter and the sero-amniotic con- 

 nection come to lie in the anterior part of the amnion in older 

 embryos. The growth in size of the amnion after being closed on<-e is 

 therefore due mostly to the enlargement of that part which is placed 

 behind the posteriiM- tube enclosing the tail end in a sî;ige like 

 Fig. 11 (PI. IL). 



In all the stages hitherto described, the head of the eml)rvo 

 projected below the level of the blastoderm covered l)v the proamnion 

 which consists only of the epiblast and hv})oblast (Fig. 41. PI. V.). 

 On this accoinit, in sections of this region, the head is found Ix'low 

 the general level of the blastoderm (Figs. ^3, 88, PI. \'., Fig. 47, PI. 

 VI.). The manner in which this anomalous state of things is 

 brought to a close, and in which the head covered by the tunnion «-on- 

 sisting of the epiblast and the somatic mesoblast comes to lie above 

 the hypoblast as in other |)arts (^f the body, has been described by 

 Strahl (No. 5) and Hoffman (No. 6) and c^uite recently by Ravn (No. 9). 



