192 HIROSHI OHSHIMA 
of C. frondosa various regular stages of cleavage on the 
second day. InC.normaniand C. saxicola, as examined 
by Newth (86), the cleavage is not absolutely regular, in that 
the four blastomeres may rearrange themselves diagonally, and no 
orderly scheme could be detected in the cleavage later than the 
sixteen-cell stage. Only in a few individuals of the latter- 
named species perfect symmetry up to the sixteen-cell stage 
was met with. A very curious feature is seen in C. glacialis 
as reported by Mortensen (82, pp. 722-3). As a remark- 
able exception among echinoderms, the cleavage here is said to 
be superficial in that the divided nuclei migrate towards the 
periphery, increasing in size, and at last there is formed an 
epithelium, each nucleus being separated by a cell wall. 
9. BLASTULA. 
The blastula when free from ege-membrane floats at about 
the middle layer of the water, rotating actively by means of 
cilia. Its diameter as measured in life is about 3854. Though 
I was unable to observe its emergence from the egg-membrane, 
the presence of a wrinkled stage inside the membrane is hardly 
conceivable in view of the fact that no remarkable increase in 
size of the free-swimming blastula as compared with the em- 
bryonic blastula is to be found. The wall consists of a layer of 
very high slender cells, the vegetative pole being indicated by 
a thicker wall. In the blastocoele a coagulable fluid now appears, 
known as blastocoele jelly or ‘ Gallertkern ’ (PI. 8, figs. 5, 6, by), 
which increases in density with the growth of the embryo. 
The blastula of C. kirechsbergii is said to be still 
covered with egg-membrane (Kowalewsky, 17). In C. 
planci the blastula is formed at the end of the first day 
(Ludwig, 22, p. 605) or in ten hours (Kowalewsky, 
17, p. 3), and the cleavage ends early on the second day 
(Selenka, 45, p. 168). According to Selenka cilia arise 
here and there at the end of the first day, and when the cleavage 
is ended every cell is beset with a cilium; the embryo then 
gets out of the egg-membrane, and swims usually near the 
surface of the water. During the course of twelve hours the 
