ANNULATA. 229 



adiicrcs thereto in the Suctoria. In many Errantia the cutis devc- 

 lopes filiform and lamelliform processes, and the latter, in some 

 species (Aphroditcc), are so large and numerous as to overlap one 

 another like scales. The hairs and bristles, already mentioned, are 

 also developed, in some species, e. g. Aphrodita aculeata, so abun- 

 dantly as to give it the mammalian character of a hairy investment, 

 whence it has been called by our fishermen the " sea-mouse." The 

 hairs of this beautiful anellid reflect brilliant iridescent hues. 



In the tubicolar order the habitations are commonly formed of 

 foreign substances, as particles of sand or shells agglutinated together 

 by the raucous secretions of the worm, which is sometimes done with 

 a considerable degree of neatness and apparent skill, as in the Pecti- 

 naricB and Terehellce. The Serpula secretes a calcareous tubular 

 shell, consisting of carbonate of lime and animal matter, like the 

 shells of Mollusks ; but differing in being quite external to the inte- 

 gument, and not organically attached to the animal, which can quit 

 and i*eturn to its tube. Most species of Serpults, as the Serp. con- 

 tortuplicata, which coats the shells of oysters and other bivalves with 

 its characteristic dwelling, have a pedunculated operculum for closing 

 the entry of the tube. 



The organisation of the integument has been studied chiefly in 

 the naked Anellids. It consists, in the leech, of a strong, smooth, 

 whitish epiderm, and of a fibro-cellular corium divided into short 

 segments, and having many pigmental cells of a brown or greenish 

 colour, except in the intervals of the rings. The muscular fibres 

 have a tendinous lustre : those of the outer layer are transverse ; 

 those of the next layer cross each other diagonally, and form a fine 

 regular reticulation : beneath these are the longitudinal fasciculi, 

 which form the most conspicuous stratum. There are also other 

 smaller muscular fasciculi in the under surface of the body, besides 

 those which specially regulate the action of the terminal suckers and 



the dentated jaws {fig. 102. b). The anterior 

 border of the mouth is produced on the dorsal 

 aspect, in the medicinal and some other leeches, 

 so as to form a kind of upper lip, which com- 

 bines with the rest of the muscular and verru- 

 cose border to form a sucker. In some sea- 

 leeches {Pontohdella, Piscicola)th.e oral sucker 

 is divided by a constriction or neck fi-om the 

 Lgg,,^ body. In Branchiobdella the pharynx is pro- 



vided with a horny upper and under jaw. In 

 the genus Clepsine a protractile flexible tube, like a proboscis, can 

 be protruded from the bottom of the mouth. The mouth of the 



Q 3 



