28 K. MITSUKUKI. 



ninss of the wliitc. It seems to me that here wehnve in a 

 very primiti\e condition the strnctiu'C described by 

 Duval (No. 10) as the placenta in Birds. 



'I'he amnion in tliose later stages seems to envelope the embryo 

 tolérai)! V closely, and its cavity is no longer spacious. 



In hatching, the yolk-sac passes into the interior of the body 

 whei-e it lies for a long time — in fact for several months, for I found 

 it in young tortoises late in the spring of the year following that 

 in which they were hatched. I'he amnion is torn into shreds, but 

 the allnntnis seems to be spbt o])en by the anterior limbs of the 

 emerging embr\(> along the sero-amniotic scam — if not nlwavs, at 

 least in some cases, for I have specimens in which ihc adantois has 

 been cast away iii this manner and is uniiijinvd. The outer shell 

 whicli has Ijccomc \er\' brittle is easily In-okcn throngli and the 

 young tortoise emerges into the worhl. 



We maA' now cxaiiiinc tlie mi<'roscopic striu-tures of these 

 mend^ranes. \\e left the scro-amniori«' connection in tlic condition 

 represented in Fig. 41) (I'l. \'L). Aftci- ihat stage, as tlu; distance 

 between the amnion and the serous envelope increases and th<' con- 

 nci'tion 1)ecomes accordingly elongated in its vertical extension, the 

 epiblast cells in it become flattened in the direction perpendicidar to 

 the plane of the eoinie<M ion. Fig. 7ß (PL IX.) represents a pai'i 

 of a section of the sei-o-aininotic' connection from the saine embi-yo as 

 that from which Fig. S(i (l*L X.) is taken, 'fiie cells show decidedly 

 the flattening referred to al)ove. 



This flattening goes on more and moi'e. but I omit the inter- 

 mediate stages and proceed to tin- descri])ti(^n of the sero-amniotic 

 connection in the finished fœtal metnln-anes (Fig. 71, PI. \ II f.) 

 Figs. 78-80 (PI. TX.) are selected seclions iVom an embryo of the 

 same stage as thai rejn'csented in Figs. 71 and 71^/ (PI. \'fT[.). All 



