ANNULOSA : ANNELIDA. 2OQ 



Reproduction, also, is always effected by means of the sexes, 

 and never by fission or gemmation. 



The common Horse-leech is only provided with a few blunt 

 teeth ; but the Medicinal Leech (Sanguisuga medicinalis, fig. 

 78) has its mouth furnished with three crescentic jaws, the con- 

 vex surfaces of which are serrated with minute teeth. This 

 species is chiefly imported from Hungary, Bohemia, and Russia. 

 In Sanguisuga officinalis, also used in medicine, the abdomen 

 has numerous black spots. In both species the oral and 

 caudal extremities are narrowed before dilating into the 

 suckers, and the body has from ninety to one hundred rings. 

 The marine Pontobddla have the body tuberculated, and 

 attach themselves to the bodies of fishes, especially skates. 

 The anterior sucker is separated in these from the body by 

 a distinct constriction or neck. In the little fresh-water 

 Clepsines the anterior sucker is wanting, and there is a pro- 

 boscidiform mouth. They are found attached to the stems of 

 water-plants. 



ORDER II. OLIGOCH^ETA (Terricola), The members of 

 this order, comprising the Earth-worms (Lumbruidas) and the 

 Water-worms (Na'ididce), are distinguished by the fact that their 

 locomotive appendages are in the form of chitinous setae or 

 bristles, attached in rows to the sides and ventral surface of 

 the body. They are all hermaphrodite. The Oligochceta are 

 divided into the two groups of the Terricolce or Earth-worms, 

 and the Limicolce. or Mud-worms and Water-worms (Sanurida. 

 and Ndididce). 



In the common Earth-worm (Lumbricus) the body is cylin- 

 drical, attenuated at both extremities, and carrying in the adult 

 a thickened zone, which occupies from six to nine rings in 

 the anterior part of the body, is connected with reproduc- 

 tion, and is termed the " clitellum," or "saddle." Locomo- 

 tion is effected by eight rows of short bristles or setae, four of 

 which are placed laterally and four on the ventral surface of 

 the body; these representing the foot-tubercles of the higher 

 Annelides. The mouth is edentulous, and opens into a short 

 oesophagus, which leads to a muscular crop, or " pro-ventricu- 

 lus," succeeded by a second muscular dilatation, or gizzard. 

 The intestine is continued straight to the anus, and is con- 

 stricted in its course by numerous transverse septa, springing 

 from the walls of the perivisceral cavity. The perivisceral 

 cavity (as in all the Oligochatd) is lined by a cellular mem- 

 brane, which is continuous with a yellow cellular layer cover- 

 ing the intestine and large vessels, and which casts off its cells 

 into the perivisceral fluid. The pseudo-haemal system is well 



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