238 HIROSHI OHSHIMA 
of blastomeres occurs. Inequality in size of the blastomeres 
is met with above the thirty-two-cell stage, and the embryo is 
wrapped up within the egg-membrane until the blastula stage 
has been attained. 
7. The blastula is spherical but not wrinkled, and is now free 
from egg-membrane. It swims about by means of cilia. The 
mesenchyme-formation precedes invagination, occurring exclu- 
sively at the vegetative pole. The invagination begs the next 
morning, 
8. In a fully-formed gastrula the archenteron shows a peculiar 
twisting, enabling one to distinguish in it three parts. The 
most anterior flat part is the future hydrocoele, the second 
transverse part is the future enterocoele, and the hindermost 
tubular part is the future gut. 
9. Very late in the gastrula stage the stomodaeum makes its 
first appearance, being preceded by a thickening of the ectoderm 
at about the middle of the ventral side. Some mesenchyme cells 
seem to be formed here by the proliferation of ectodermal cells. 
The position of the stomodaeum is, as can be shown in later 
stages, a little on the left of the median line. 
10. The dipleurula stage begins late on the second day. In 
this stage the hydro-enterocoele first becomes separated from 
the gut. The former then divides into the hydrocoele and 
enterocoele. The hydrocoele produces the rudiment of the 
pore-canal directed postero-dorsad, and six lobes on the anterior 
expanded margin. ‘These latter are rudiments of the five primary 
tentacles and of the mid-ventral radial canal. The enterocoele 
divides into right and left vesicles, situated on the left dorsal 
and antero-ventral sides respectively. 
11. On the third day doliolaria is formed, which is charac- 
terized by the possession of three ciliary bands around the 
posterior half of the body besides the weaker uniform ciliation 
over the pre-oral hood and on the anal field. From the hydro- 
coele are first differentiated the mid-ventral radial canal and 
four of the primary tentacles. 
12. The primary pair of pedicels make their appearance as 
ectodermal depressions (pedal pits) situated between the second 
