240 



THE STUDY OF ANIMAL LIFE CHAP. 



podia, and eyes and tentacles and gills, but there is much 

 difference between those which swim freely in the sea 

 (e.g. Alciope and Tomopteris and some Nereids) and the 

 lobworms which burrow and make countless castings upon 

 the flat sandy shores, or those which inhabit tubes of lime 

 or sandy particles (e.g. Serpula, Spirorbis, and Lanice or 

 Terebella conchilega). The earthworms with compara- 





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FIG. 68. A BUDDING MARINE WORM (Syllis ramosa). 

 (From Evolution of Sex ; after M'Intosh's Challenger Report.) 



tively few bristles (Oligochaeta) are hermaphrodite, 

 while almost all the marine worms with many bristles 

 (Polychseta) have separate sexes. Moreover, those of 

 the first series usually lay their eggs in cocoons, within 

 which the embryos develop without any metamorphosis, 

 while the sea-worms, though they sometimes form cocoons, 

 have free -swimming larvae usually very different from the 

 adults little barrel-shaped or pear-shaped ciliated 

 creatures known as Trochospheres. 



