190 HIROSHI OHSHIMA 
the tentacles of the mother is, accordmg to Newth (86, 
p. 633), undergoing or has just completed the second matura- 
tion division. In the egg of Holothuria floridana 
Kdwards (12) saw three polar bodies, one of which was 
remarkably larger than the others. 
Fertilization.—The sperm head is still minute and 
stains intensely ; it measures about 2-5 in diameter. It 
is found situated rather peripherally and quite distant from the 
animal pole, and rather near the equator (Pl. 8, fig. 4, sp), 
so that it is doubtful whether it is at the animal pole that the 
Spermatozoon penetrates into the egg. It is highly probable 
that the spermatozoon enters the egg after, or at the same 
time as, the protrusion of the first polar body. In some sections 
the sperm nucleus is seen approaching the centre of the egg 
and becoming somewhat vesicular. In an egg fixed at fifty 
minutes after being shed the sperm nucleus is found lying 
close to the ege nucleus ; it is of the same size as the latter and 
encircled with astral rays. 
8. CLEAVAGE. 
Among the eggs fixed fifty minutes after being shed were 
found some showing the first cleavage spindle lying horizontally 
at the centre of the ege. Thus the first cleavage seems to begin 
in about an hour. The amount of the material which I was 
fortunate to rear was so limited that, from fear of destroying 
the whole culture or in any case of losing much before any further 
development could be observed, I was unable to examine closely 
the living embryos during cleavage, &c. The following state- 
ments are given from preserved materials. 
The eggs fixed within two and a half to three hours after being 
shed show various stages between four-cell and thirty-two-cell 
Stages. 
Four-Cell stage.—The blastomeres are equal in size, 
elongated along the egg-axis, and flattened or even slightly 
concave on the axial surface. Usually the blastomeres inter- 
1 The sperm head before entering the egg measures about 2 in diameter. 
