1 88 WORMS. 



according to others, the larval characteristics are adaptive to the mode 

 of life, and without historic importance. 



ProtodrUus is even smaller than Polygordius, with more cilia, mobile 

 tentacles, and two fixing lobes on the posterior extremity ; the move- 

 ments are Turbellarian-like, the reproductive organs hermaphrodite, 

 the development direct. Histriodrilus is parasitic on the eggs of the 

 lobster. 



Appendix (2) to Chistopoda. 



Parasitic and Degenerate Ch^topods. Myzostomata. 



The remarkable forms (^Myzostomd) included in this small class, live 

 parasitically on feather-stars, on which they form galls. They are regarded 

 as divergent offshoots from primitive Annelids, the larval form showing 

 some distinctly Chaetopod characters. The minute disc-like body is 

 unsegmented, and bears five pairs of parapodia, each with a grappling 

 hook, with which five pairs of suckers usually alternate. There are also 

 abundant cirri. The skin is thick, the body muscular, the nervous 

 system is concentrated in a ganglionic mass, which encircles the gullet 

 and gives off abundant branches. There is a protnisible proboscis and 

 a branched gut ; the mouth and anus are ventral. The ova arise in the 

 reduced body-cavity, and pass out by the anal aperture, via three 

 meandering oviducts. The testes are paired, branched, and ventral, 

 with associated ducts, which open anteriorly on the side of the body. 

 The sexual relations are interesting, for one species is hermaphrodite and 

 another unisexual, between which there is an intermediate species with 

 ovaries and rudimentary testes. The hermaphrodite form may bear on 

 its body dwarfish males, analogous to the complemental pigmies on 

 some hermaphrodite barnacles. 



Class DiscoPHORA or Hirudinea. Leeches. 



Most leeches are worm-like aquatic animals, with blood- 

 sucking propensities, but some live in moist soil, and others 

 keep to the open surface, while the parasitic " vampire " 

 habit, familiarly illustrated by the apothecary's ancient 

 panacea, is in many cases replaced by carnivorous habits and 

 predacious life. The medicinal leech {Ifirudo) is typical of 

 the majority, for it lives in ponds and marshes, and sucks 

 the blood of snails, fishes, frogs, or of larger available 

 victims. The giant leech {Macrobddla valdiviana), said to 

 measure 2\ feet in length, is subterranean and carnivorous, 

 while the wiry land-leeches {ffamadipsa, etc.), of Ceylon 

 and other parts of the East move in rapid somersaults along 



