ANT) THE FOETAI, MEMBKAXKS. [X THE ('Hiriv. 



:53!) 



been engaged in elucidating these points in fhe history of the foetal 

 inenil)runes of the chick and ha\e hi-ought to light some facts which 

 appear to me very remarkable. The present article contains the main 

 results of my investigation. 



Before going further, I wish to express my best thanks to my 

 teacher-, Profs. Dr. Mitsukuri jind Ijima, for their constant encourage- 

 ment and advice throuHiout this investig-ation. 



Dia^. / 



25-30 Hours. 



1. Orujui of llie Scrit-AmuKAic Connection. 



If we examine a chick embryo of 2o-o0 hours (Diag. 1) we 

 find that the extra-embryonic coelomic cavities (E) have already 

 Diaé. 3, extended themselves on l)oth sides, 



some distance in front of the embryo 

 itself. These anterior parts of the ex- 

 tra-embryonic coelomic cavities have 

 not, however, yet extended themselves 

 directly in front of the head, and 

 leave here a sort of Ijay (P), where 



40-45 Hours. 



Head not represented the hypoblast and tlie ej^blast alone 

 Diaè. 2. Diag. 4, are as yet present. 



When the embryo has become 

 30-40 hours old (Diag. l>), the an- 

 terior limbs of the extra-embryonic 

 coelomic cavities meet in front of the 

 head, cutting off the ])revious bay 

 from the region in front. Thus an 

 area (P), which is formed by the 

 hypoblast and the epiblast only, has 

 )>een circumscribed just in front of, and beneath, the head. This is 



30-40 Hours. 



Longitudinal sectidii 



through a line, x y 



(Diag. 3). Heart 



not reprei-euted. 



Ö. — Sinus termimiHs. 



P. — Proamnion. 



H.— Head. 



E. — Extra-embryonic coelomic cavity. 



M. — Mesoblastic septum. 



F. — Amniotic fold. 



