16 K. MITSUKURI. 



How the proamnion hns been eneronched upon from both sides and 

 has all but disap'H'ared is \ ery clear, if we compare these two ügures. 

 These two figures show also that the k^ft \'itelliiie vein (Y va) becomes 

 much larger than the right. 



h. TrioHijx Japonicus. 



Earlier stages in the development of the Amnion in Tri onyx 

 are verv much as in Glemmys. There is in fact n<j point of any 

 impcn'tance which is different in the two species. As, however, tlie 

 Trionyx embryos in ni}' possession show very well in surface views 

 how the extra-embryonic cœlomic cavities arise first in the neck region 

 and gradually spread backward, I shall introduce here some figures 

 which illustrate that point among others. 



Fig. 16 (PL III.) is the stage closely resembh'ng Fig. 1 of 

 Clemmys (PI. I.). The anterior horse-shoe sha})ed groove (" die 

 vordere (Trenzfruche "), the still open medullary canal, and the trans- 

 parent area in front of the embryo are all very similar to the 

 Clemmys embryo < )f the corresponding stage. 



In Fig. 17 (PI. III.) the amnion has extended over the anterior 

 half of the embryo. When seen from the ventral side the whole anterior 

 end of the embiyo covered by the proamnion is projecting below the 

 level of the blastoderm, as shown in Fig. 17^. In the neck region where 

 the emljrvo gains tlie level of the blastoderm, one is able to recognize 

 distinctly the extra-embryonic cœlomic cavity on each side of the 

 embryo appearing as a vesicle which bulges out the dorsal and ventral 

 surfaces of the blastoderm (Figs. 17 and 17a). The level of its poster- 

 ior limit is the same as that of the posterior limit of the amnion, and the 

 growth backward of the cœlomic cavities progresses hand in hand with 

 the backward growth of the amnion. fhese t\vo cavities, one on each 

 side of the embryo, are (jf course the same as Strahl's '' Mesublastische 



