36 K. MITSUKURI. 



curately the succession of the changes that take place. 



On the present occasion, I shall not touch on the formation of 

 the mesoblast or mesenchynia at the periphery of the blastoderm an 

 account of which, I reserve for a future paper. 



Clemmys japonica, Gray. 



The earliest stage in my possession was obtained from the eggs 

 opened directly after they were deposited. The blastodermic region, 

 owing to its lighter specific gravity, is always found at the upper pole, 

 in whatever position an egg may happen to have been deposited. 

 Surface views of the blastoderm are represented in Figs. 1 and la 

 (PL II). It corresponds to that shown in Figs, la and lb of the paper 

 on Tri onyx (No. 1) but is somewhat younger. The blastoderm 

 shows a comparatively large pellucid area, in which the embryonic 

 shield is placed excentrically, nearer its posterior edge, and is joined to 

 this edge by irregular opat^ue patches. The most conspicuous 

 feature in the dorsal view of the embryonic shield (Fig. 1) is the 

 dorsal opening of the blastoporic passage. It is placed in the 

 median line near the posterior end of the shield, and is a crescent- 

 shaped, transverse slit, the concavity being to the front. The 

 embryonic shield shows indistinctly two concentric zones which are 

 most marked in front and at the sides. The innermost area is the 

 most opaque part of the blastoderm. Xear the front edge of this area, 

 there is however a somewhat less opaque area which corresponds, it 

 will be seen, on referring to the ventral view (Fig. la), to the ventral 

 opening of the blastoporic passage. In the same view (Fig. la), the 

 innermost ;ind most opaque area is seen to be the thick part through 

 which the l)lastoporic passage leads from the dorsal to the ventral 

 opening. 



The minute structure of this early stage will become clear from 



