8 K. MITSÜKURT. 



eclo"e of tile aiiuiinii is roachod, and, oradn.'illy Icssciiiiif^' in \hv\r height, 

 arc lost too'ethor with tin- uratliially lowcrini;' lat^-i-al iolds of tlie 

 amnion. Tlius the niosohlast now has a consi(]('ral)l<' share in the 

 formation of the amnion. 



Fio-s. 34-38 (PK V.) are a series of transverse .sections selected 

 from different regions of tliis embryo. 



Fip-. 34 is from the reo-ion where the lateral folds of tlie amnion 

 are still Ioav. When we compare this with Fio-. 30. we see that in 

 this stage the somatic layer of the mesoblast is f<^ldetl and pushing 

 itself into the hitherto solid epiblastic amniotic folds. 



Fig. 35 is from the region where the mesoblastic folds or, wliat 

 amounts to the same thing, the extra-embryonic cœlomic cavities are 

 still some distance from the median line. Fig. 35 a represents the 

 median dnfsal portion •»!' the amnion in the same section under a 

 liiiidier ])owei-. It is evident that here also, a somatic fold ol' the 

 mesoblast insinuating itself, so to speak, on each side into iho ori- 

 ginally solid epiblastic amnion is separating the latter into two liml)s 

 of which the inner is the true amnion and the outer the false amnion* 

 or serous envelope. 



In Figs. 36 and 36 a, the mesoblastic folds have reached furtlier 

 dorsahvard, but the amnion aiid the serous envelo])e are unite(l in the 

 mc^dian line. \n Fig. 3(! /*, a few >ections forwai-d ol" Fig. ."»(!. the 

 mcsolilastic folds have readied still fiirthcj' dorsal ward— the most 

 (h)rsalward at this stage — but still there is a distinct connection be- 

 tween the amni<m and the serous envelo])e. 



The mesoblastic folds inaintain themselves at the level given in 

 Fig. 36 /' for many sections forw^ard, and the comiection between the 



UTl' 



* In futniv, I shall avoid iisint;- tho t^riii " fais.- amnion "" to d.'iiotu the strurtnit' 1 

 indicated and shall call it tlip sorons .'nvelope, as tlio tonn -'fnlsi' nniiiinTr' is appli.'d \>> tu 

 very different structures }jy GJerman and Enolish authors. 



