178 HIROSHI OHSHIMA 
plankton. Among pedate holothurians, the forms which offer 
the materials for the study of embryology belong to two families 
only, i.e. Holothuriidae and Cucumariidae, both of which are 
chiefly dwellers in shallow water. Ostergren (42, 1912, 
p. 338) attributed the shortness of larval life im Cucumariidae 
to the fact that they live near the coast. Any longer period 
of larval life, he thought, would expose the larvae to greater 
danger of being swept away by violent currents to destruction. 
Again, our knowledge of their development is fragmentary, 
because, first, many of the observations have been made on those 
forms which have brooding habits in which it is not easy to 
secure a complete series of developmental stages, and, secondly, 
there are some difficulties in the technique of investigation, the 
eggs being yolky and the larvae mostly opaque. 
The embryology of pedate holothurians was first studied by 
Danielssen and Koren (11, 1856). Their material was 
identified as Holothuria tremula, but Ludwig (21, 
1889-92, pp. 249, 251) and Mortensen (838, 1898, p. 24) 
alike denied this and suggested that it was dendrochirote. Later, 
Louis des Arts (2, 1910, pp. 9-10) and Ostergren (42, 
1912, p. 388) have both identified it as Cucumaria fron- 
dosa. Kowalewsky (17%, 1867) was the second who had 
the good fortune to observe the spawning of C. planei 
(=Pentacta doliolum) and C. kirchsbergii (=Pso- 
linus brevis); he managed to rear larvae for over ten 
days, which attained the pentactula with a pair of primary 
pedicels. 
Selenka’s work (45, 1876) on Holothuria tubulosa 
and Cucumaria planci (=C. doliolum) entered into 
a more detailed account than those of his forerunners, since 
he employed the paraffin-section method. Ludwig (22, 
1891) most excellently explained the processes of organ forma- 
tion, and elucidated many points upon the origin of various 
organs in ©. planci. He escaped the failure which befell 
Selenka, since he was successful in obtaining well-orientated 
serial sections, whereas Selenka adopted the method of 
‘ Masseneinbettung ’, i.e. embedding large numbers of embryos 
