ECHINODERMATA 419 



attains a length of 6 mm. and is characterized by the complicated form of 

 its ciliated band, has been recently described by Chun (No. VII., Appendix 

 to Literature). The ciliated band of this larva is extraordinarily tortuous, 

 and exhibits arabesque-like foldings. Somewhat similar conditions were 

 previously mentioned in the case of a very large Tornaria. Chun's 

 paper, which is important in many respects, contains an account — to 

 which attention may be called here— of a sac-like invagination of the 

 hind-gut of the larva, from which, according to Chun's conjecture, the 

 respiratory trees of the Holothurian may arise. — K. ] 



The Aaricularia larva does not occur in all the Holo- 

 thurioidea. Thus, for instance, the larva of Cucumaria 

 doUolum at the time of the formation of the mouth assumes 

 a cylindrical form (Selenka). The flagella disappear zone 

 by zone, until the larva retains only four to five bands of 

 cilia, a ciliated anal area, and a ciliated cephalic zone. With 

 this the so-called pupal stage is reached, which does not make 

 its appearance in the development of other Holothurians 

 until later (comp. p. 427). Another Holothurian, Psolinus 

 hrevis, develops, according to Kowalevskt (No. 28), alto- 

 gether without a metamorphosis. The young Holothurians 

 arise directly from the eggs, which are laid in the sea- water. 

 In Phyllopliorus urna the larvoe, which are pi-obably com- 

 pletely and uniformly ciliated, are said to swim about in the 

 body cavity of the parent. When they abandon the parent, 

 they already possess five tentacles and two feet. A similar 

 condition is found, according to Ludwig (No. 33), in the 

 likewise viviparous Chirodota rotifera. 



Asteroidea. — The larval form of the Asteroidea, like 

 that of the Holothurioidea, can be derived from the funda- 

 mental form. If Figs. 200 B and 198 (7, from JoH. Muller's 

 diagrams, are compared, one sees that in the Asteroid larva 

 the preoral area of the ventral surfaces, together with the 

 part of the ciliated band surrounding it, is isolated. The de- 

 pression on the ventral surface is continued farther forward 

 here than in the Holothurian larva. In this way the con- 

 nection of the preoral area with the dorsal surface is inter- 

 rupted, and the ciliated band is separated into two parts. 

 Thus two ciliated bands arise, which, from their positions, 

 may be designated as the adoral and adanal (Figs. 200 A 



