444 



WORMS. 



Different species of the genus Clepsine may be found on the leaves of water- 

 plants and on the under side of stones. They are grey, yellow, or whitish in 

 colour. Instead of burying their eggs like the medicinal leech, these creatures 

 carry them about, and the young after birth remain some time with their mother. 

 They live principally upon water-snails and young mussels. The engraving 

 on p. 443 represents the rock-leech, Pontobdella muricata, remarkable for being 

 an inhabitant of the sea, and also for having the skin covered with warts and 

 knobs. The body, which gradually narrows from the posterior end to the head 

 is of a greenish grey colour, and the anterior sucker large and button-shaped. 

 During the daytime these leeches usually rest partially coiled up, as shown in the 

 lower figure, and firmly attached by their hinder sucker to some rock ; but their 

 muscular strength is so great that they are able to maintain themselves extended 

 in an almost horizontal direction, as represented in the upper figure of the illus- 

 tration. They feed upon skates and other fish. 



The Gephyrean Worms, — Class Gephyrea. 



Gephyreans are marine, cylindrical, worm-like animals, presenting no distinct 

 external segmentation of the body, and possessing nothing of the nature of limbs or 



gills. The skin is horny, 

 though not calcareous, and 

 often provided with tuber- 

 cles, hooks, or bristles. The 

 anterior end of the body is 

 furnished with a retractile 

 and sometimes highly- 

 flexible proboscis, at the 

 end or at the base of which 

 the mouth is situated ; the 

 alimentary canal either 

 traverses the body from end 

 to end, as in Bonellia and 

 Echiurus, or is coiled round 

 a special spindle muscle, and 

 returns upon its course to 

 open in the front half of the 

 body,as in Sipunculus,Phas- 

 colosoma, and Phymosoma. 

 In the last-named genus the 

 head is furnished with a 

 circle or half -circle of 

 tentacles. The muscular, 

 vascular, and nervous 

 systems are well-developed; 

 the latter consisting of a 



A, Bonellia; B, Phascolosoma; C, Priapulus. (Nat. size.) Cerebral ganglion, an 03S0- 



