NOxzZziW i ChRODE OCTOPUS GRYELLOTALPA COSTA, 315 
The £F group and the micromeres divide only vertically. 
The ventral plate is formed by the descendants of the large 
macromeres and of the £F group, and has an oblique position 
upon the egg, owing to the obliquity of the second cleavage 
plane. 
After the 42-cell stage two cells are found in the interior of 
the egg in different stages of disintegration. 
Formation of the Embryo. 
In the last section I have described the ventral plate as being 
formed by the macromeres on the lower pole of the egg. I 
am well aware that in this I stand alone, all previous writers 
describing the descendants of the micromeres as the first which 
rise to the surface. Further, they describe the embryo as 
forming over the micromere pole, and the macromeres as 
gradually added to the outer layer during the growth of the 
ventral plate over the egg. Della Valle, who studied Microdeu- 
topus as a control observation, agrees in this point with what 
has heretofore been published. He describes the blastoderm as 
arising on the micromere pole in Orchestia, and makes no ex- 
ception in the case of Microdeutopus. The results which 
Mlle. Wagner obtained for Melita agree most nearly with 
what I found for Microdeutopus. According to her account, 
when the cells emerge from the yolk they lie on the sides as 
well as on the oral pole of the egg, and later grow over 
the dorsal face. This corresponds almost exactly to what I 
have found. The figures 4, 5, and 6 of Sunamphitoé, by Mlle. 
Rossiiskaya, are almost identical to those I have for sections 
of eggs in the stage figured on Pl. XXVI, Fig. 17. Her figures 
show that the blastoderm probably arises in the same way as 
in Microdeutopus. 
The EF group lies above the plane of the equator on the 
side of the micromeres, and the cells of this group are the first 
which appear on the surface to form the blastoderm. Previous 
investigators may have been led by this to suppose that the 
ventral plate forms on the micromere pole, but, having traced 
the development cell by cell on the stained and cleared egg, I 
