162 ANNELIDA [CH. 



ramifying network of chambers opening by minute pores on the 

 testis lobe. 



The other systems of organs are still more unlike what has been 

 described in the case of the earthworm and deserve a short account. 

 Leeches live by sucking the blood or juices of other animals, 

 usually of Vertebrates. They are divided into two large groups 

 (a) the RHYNCHOBDELLIDAE, which pierce the tissues of their hosts 

 by means of a fine protrusible stomodaeum, the so-called proboscis, 

 and (6) the GNATHOBDELLIDAE, which bite their prey by means 

 of horny jaws. The medicinal leech is one that bites, and the 

 triradiate little scar which its three teeth make in the skin was 

 well-known to our forefathers in the times of bleeding and cupping. 

 The three teeth, which are notched like a saw, are really only 

 thickenings of the cuticle borne by the wall of the pharynx, which 

 contains many unicellular glands whose secretion prevents blood 

 from coagulating. Thus the leech when fixed on to its victim by 

 the oral sucker readily obtains a full meal. 



From the pharynx a short narrow tube, the oesophagus, leads 

 into an enormous dilatation, the crop. This extends to the four- 

 teenth segment and gives off on each side a series of eleven pouches 

 or caeca (Lat. caecum, blind) which increase in size from before 

 backward. The posterior caeca are very large and reach back to 

 the level of the anus, lying one on each side of the intestine. The 

 leech has the habits of a boa-constrictor. It makes a hearty meal, 

 absorbing as much as three times its own weight of blood, and the 

 blood it absorbs is stored up for many months in this enormous 

 crop.. It slowly digests the food in a small globular stomach 

 situated just behind where the posterior caeca leave the crop. The 

 stomach opens into a short intestine which ends in the anus, a 

 minute pore situated dorsally between the posterior sucker and the 

 body (Fig. 68). 



In one genus at least, Acanthobdella, the coelomic cavity is 

 almost as well-developed as in an earthworm, and is 



Coelom. . 



divided up by septa as in that animal, but in other 

 leeches the cavity tends to disappear, becoming in fact filled up 

 by a great growth of tissue, and thus reduced to a few narrow 

 channels. In many leeches it contains a fluid closely resembling 

 the true blood, so that unless very careful microscopic examination 

 be made these channels may be mistaken for true blood-vessels. 

 The capsules in which the ovaries and testes lie are also parts of 

 the coeloin. 



