42 ART. 3. — S. IKEDA : CONTRIBUTIONS 



dermal, and the neural layers of the epiblast). The shaded 

 portions on both sides of the segmentation cavity arc the sections 

 of the equatorial zone. Fig. 62 gives a magnified view of the 

 roof drawn from another section of the same series : the cells of 

 the outer layer are somewhat flattened and slightly smaller than 

 those of the inner layer. As before mentioned, this extreme 

 tenuity of the roof accounts for the translucency of the area of 

 the segmentation cavity in an external view. 



Fig. 54 is the median sagittal section of an egg correspond- 

 ing to Figs. 10 and 11 or to Figs. 26 and 27 of Egg C. The 

 blastopore lip has already closed in a circle and is at the same 

 level all around. 



The next two figures (Figs. 55 and 56) are respectively a 

 median sagittal, and a middle transverse section of the eggs cor- 

 responding to that represented in Fig. 12 or in Figs. 28-30 of 

 Egg C in which the rotation of the egg has commenced. The 

 archenteron has acquired a distinct lumen along the posterior and 

 dorsal surface of the yolk-mass, while the segmentation cavity 

 has become pushed forward and diminished in size in an inverse 

 ratio to the enlargement of the first named cavity. 



Fig. 57 is a median sagittal section of an egg corresponding 

 to Fig. 13 or to Figs. 32 and 33, in which the blastopore has 

 become moderately closed and the rotation has progressed con- 

 siderably. The segmentation cavity has now vanished, leaving only 

 small irregular cavities at the anterior end of the large archenteric 

 cavity. This accounts for the fact that the translucent area can 

 no longer be recognized in a superficial view. 



Figs. 58 and 59 give respectively a median sagittal, and a 

 middle transverse section of the stage represented in Fig. 14 or 

 in Figs. 36 and 37. Here the blastopore is on the point of being 



