PELAGIC ZONE SURFACE LIFE 451 



p. 425) that a great many species lay floating eggs, and these, 

 together with the transparent larvae that hatch out of them, 

 belong to the plankton fauna. Primitive Vertebrates (Proto- 

 chordatd] are abundantly represented by certain Sea- Squirts or 

 Ascidians (Urochorda), including some little tadpole-shaped forms 

 (Appendicularia^ &c.), Barrel Ascidians (Doliolum), Salps (Salpd), 

 and Fire-Cylinders (Pyrosoma), all of which have received notice 



Fig. 1306. Wing-Footed Snails (Pteropoda]. A, Cuvierina; B, Clio; c, Creseis; D, shell of Cleodora; E, Limacina; 

 F, Clione; G, Halopsyche: H, front part of Pneumoderma, with hook-bearing tubes and groups of stalked suckers, for 

 securing prey. A-E, Shell-bearing forms; F-H, shell-less forms. 



in earlier sections (see vol. i, p. 299; vol. iii, pp. 38 and 422; and 

 p. 1 06 of present volume). 



Plankton Molluscs (Mollusca). The beautiful Violet -Snail 

 (lanthina), with its egg-raft, belongs here, also the members of 

 the remarkable and diversified group of Fin-Footed Snails (Hetero- 

 poda), and a curious little Sea- Slug (Phyllirhoe), which is flattened 

 from side to side (see vol. iii, pp. 34 and 36). Far more 

 characteristic than these, however, are the little Wing-Footed 

 Snails (Pteropoda, fig. 1306), which are often found associated 

 in vast shoals, affording an important contribution to the bill of 

 fare of animals so large as Whales. 



