NEMERTINE WORMS 



419 



holes in the rock. Most readers will recollect the somewhat 

 melodramatic account given by Victor Hugo (in The Toilers of 

 the Sea) of an encounter with a gigantic animal of the sort. 



LIFE-HISTORIES, &c., OF NEMERTINE WORMS (Nemertea) 



The unsegmented ciliated worms included in this group are 

 usually of rounded shape, and the vast majority of them are 

 marine, though some few live 

 in fresh water or on the land. 

 Their structure has elsewhere 

 been described (see vol. i, p. 

 305). Some Nemertines are 

 quite small, but others may be 

 many yards in length. 



The marine forms are for 

 the most part oviparous, and lay 

 their eggs either singly or in 

 clumps, surrounded by a gela- 

 tinous substance, much as in 

 some of the molluscs. Develop- 

 ment may be either direct or in- 

 direct, and in the latter case the 

 larva which issues from the egg 

 is often of the kind known as a 



Pilidium (fig. 945), which resembles an antique helmet in shape, 

 and is like a trochosphere in some respects. The adult worm 

 comes into existence by the ingrowth of four depressions of 

 the skin, which surround the digestive tube. The remaining 

 organs are gradually formed, and the metamorphosis is com- 

 pleted by the larval skin being thrown off A few Nemertines 

 are viviparous, the eggs developing internally, and in this case 

 there is no larval stasfe. 



The majority of marine forms live in shallow water among 

 corals or sea-weeds, round which they twine their bodies. Many 

 may be found under stones near low-water mark. A few species 

 live in tubes, formed by the hardening of a fluid which exudes 

 from the skin into a membranous or gelatinous substance. 

 Others appropriate the empty shells of molluscs as dwellings, 

 and some kinds excavate burrows for the same purpose. 



Fig. 945 — Pilidium Larva from the right side, enlarged. 

 c, Ciliated band; d., two of the four disc-like ingrowths 

 to form the young worm (the other two are seen to the 

 left}: /., intestine; /., side-lappet. 



