148 



THE FOOD OF ANIMALS 



lating manner or by creeping with the aid of its suckers, which 

 are alternately attached to the surface upon which it progresses. 

 Although devoid of the obvious feeler-like structures seen in 

 such a worm as the sea-centipede, it is nevertheless richly pro- 

 vided with organs of sense, there being transverse rows of tactile 

 structures on the upper surface, and a number of peculiar eyes 

 on the upper margin of the head. Attaching itself by the front 

 sucker to the body of its victim, it cuts through the skin with 



Fig. 407. — Structure of Medicinal Leech {Hirudo medicinalis) 



A, Dissection from side: 7n.s. mouth-sucker; p.s. hind sucker; y. a jaw; ph. pharynx: gl. gullet; i-ii, 

 pouches of crop; st. stomach; int. intestine; br. brain; jL.r. nerve-ring; gl and^2_?, first and last ganglia 

 of ventral cord. B, Mouth-sucker cut open from below, showing the three jaws, _/'. j. j. c, A jaw with 

 its muscles and saw-like edge, d. Three-rayed bite, c and d much enlarged. 



three horny saw-edged jaws that project into the beginning of 

 its digestive tube, the result being a three-rayed incision ad- 

 mirably adapted for the exit of blood, which is pumped out by 

 means of the muscular pharynx, that alternately dilates and 

 contracts so as to constitute a sort of suction-pump. It should 

 further be added that a number of small glands open into the 

 pharynx and pour out a fluid which prevents the blood from 

 clotting, as otherwise the sucking process would be hindered. 

 The greater part of the food-tube consists of a very large crop, 

 the sides of which are drawn out into pairs of pouches, an ar- 

 rangement which permits a large quantity of blood to be stored 

 up for leisurely digestion. It is therefore not surprising that a 

 single full meal goes a long way. 



Blood-sucking Leeches are by no means limited to an aquatic 

 life, and it is notorious that in tropical regions innumerable Land- 

 Leeches harbour among damp vegetation, from which they sally 

 forth to attack all sorts of warm-blooded animals, human beings 

 not excepted. Many travellers have given vivid accounts of the 

 operations of these unpleasant creatures. 



