i86 WORMS. 



other animals, and have sharp " horny jaws," while the anterior part of 

 the gut is protrusible as a proboscis. 



Nereis and Nephthys are two common genera, species of which may 

 be unearthed by digging in the sand close to rocks, though at times 

 these or other species are seen swimming freely. The sea-mouse, 

 Aphrodite, has iridescent bristles, a feltwork of matted hair covering 

 large gill-plates which lie along its back, a very large muscular pharynx, 

 and a gut with numerous irregular branches extending throughout the 

 body. A very common shore form a little like a small Aphrodite is 

 Polynoe. As an actively errant worm, with well-developed eyes, Alciope 

 may be noted, and the family of Syllids is remarkable for the unusually 

 prolific asexual budding, which sometimes results in a chain or even an 

 irregular branched aggregate of individuals. As the cuticle is often 

 iridescent, and as the red blood may shine through the skin, these marine 

 worms are frequently beautiful. The list of nymphs and goddesses has 

 been the source of such titles as Nereis, Aphrodite, Eunice, and Her- 

 mione, and one can almost believe the legend, according to which a 

 specialist on Errantia christened his daughters after his seven favourites. 



(b) Other marine Polychseta, however, lead a more sluggish life 

 within various kinds of tubes, limy, sandy, papery, or gelatinous. As 

 one would expect, their parapodia are minute, apt to degenerate, and 

 often used solely for clambering within the tube. The pre-oral region 

 is small, but the anterior rings usually bear gills, cirri, and tentacles, 

 often in rich profusion. These Sedentaria rarely have a protrusible 

 pharynx, and never "jaws." Most of them feed on minute Algas swept 

 in by the cilia on the tentacles and other structures about the mouth. 



The fisherman's lob-worm (Arenicola piscatorum) burrows in the 

 sand like Lumbricm on shore, and forms the familiar castings on flat 

 beaches. Its parapodia are much reduced, and the body is markedly 

 divisible into a swollen anterior, a gill-bearing median, and a narrower 

 posterior region. Common also on the shore within a tube of glued 

 sand particles is Tercbella or Lanice conchilega, where the excretory 

 tubes are partly united by a longitudinal tube in a manner suggestive of 

 the segmental duct which connects the nephridia of a young Vertebrate. 

 The twisted limy tubes oi Serpula are common outside shells and all 

 sorts of marine objects, and the animal bears a stopper or operculum, 

 with which it closes the mouth of its tube, but through which it 

 probably at the same time breathes. In deep water, within a yellow 

 parchment-like tube, Chcetopterus may be dredged, perhaps the strangest 

 form of all. ° 



III. Echiuridm. 



In holes in the rocks on some of the warmer European coasts lives a 

 curious " worm "—Bonellia viridis, of a beautiful green colour with „. 

 globular body and a long, grooved, anteriorly forked, pre-oral pro- 

 trusion. Such at least is the female, but the male is microsopic in size 

 hopelessly degenerate, and lives parasitically in or on its mate The 

 male resembles in some ways a Turbellarian, is mouthless and gutless 

 and little else than a migratory spermatophore. By means of cilia it 

 moves from one part of the female to another, and fertilises the eggs' in 



