ON TUE FOETAL MEMBRANES OF CHELONIA. 9 



aiTinion and the serous enveloj)e is also iuvariahly jn-eseiit. (Coinjtare 

 Fig. 3, PI. [.). 



In Figs. 37 .'ind o7 a, which arc froii) the region of the he;irt, 

 where the head-end is heuiiiniiig ti) sink heh)\v tlic sm-face of the I)histo- 

 derm, the mesoblastic folds have again receded fi-om each other and the 

 connection l)eMveen the amnion and the serous enveioi)e is a^ain liroad. 



Fig. 38 is from tlie .legion of the head sunk l)e]o\v ihe le\el of the 

 bhist()der!n, which therefore ;i|)])ears above tlie liead in this s(^ctiorj. Tiie 

 amnion or proamnion consists only of the epildast and hypoblast. 



The relations of different parts will become clearer, when studied 

 in a longitudinal section. 



Fig. 41 (PI. V.) is such a section slightly out of the median dorsal 

 line so that the extra-embrvonic cœlomic cavity fcœl') of one side 

 appears in the amnion. This section shows that the epiblastic amniotic 

 fold reaches nearly to the neiu-enteric canal, while the hypcjblastic fold 

 extends only to the neck region. The triangidar space between these 

 two f(jlds as seen in this section is occupied, for the most part, by the 

 mesoblast enclosing a porticjn of the extra-embryonic cœhjmic cavity. 

 A little earlier there would have been no mes(jblast in the amnion 

 which then consisted, in the dorsal region, of the epiblast only, and 

 in the sunken head part, of the epiblast and hy|)oblast. The meso- 

 blast is now ])ushing itself into the solid epiblastic sheet of the 

 amnion, dividing it into an outer and an inner lindo. In Fig. 41, the 

 posterior ])art of the epiblastic fcjld is, however, still solid. Anteriorly 

 the mesoblast is insinuating itself between the epiblast and hypoblast. 

 The cœlomic cavity in the mesoblast is widest in the anterior part. 



One of my most important results is in regard to the connec- 

 tion between the amnion and the serous envelope, seen in Figs. 

 35-37. Contrai-y to what is hithert(3 known, the extra- 

 em b r y o n i c c ( e 1 o ni i c c a V i t i e s of t w (j sides a r e n e v^ er united 



