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AN NU LATA AND HIRUDINEA 



A great many tropical countries appear to be plagued with leeches 

 which affect men and animals as indicated above, but it is prob- 

 able that Algeria, Palestine, and Ceylon are the most infested. 

 Among the other places in which they are troublesome may be 

 mentioned the Philippines, Java, Sumatra, Australia, Japan, and 

 Chili. In Algeria and Palestine the leech lives in the pools of 

 drinking-water, and here the endoparasitic form may be met with ; 

 whereas in Ceylon it is usually a land leech which attacks the 

 individual, and therefore the ectoparasitic condition is common, 

 while the endoparasitic is more rare, being due to Hirudo multi- 

 striata. 



Morphology. — Leeches have an elongated, more or less oval body, which 

 is very retractile and extensile, and is marked by annuli or rings, of which 

 several — usually five — form a somite. The number of rings to a somite is, 

 however, reduced anteriorly and posteriorly, being abbreviated. At the 

 anterior extremity is the oral sucker, and at the posterior the acetabulum. 

 The skin possesses many unicellular dermal glands. The mouth-opening is 

 situate in the anterior sucker, and the anus either in or just in front of the 

 constriction which separates the posterior sucker from the body. 



The male genital opening is placed on the twenty-fourth annulus, and the 

 female five annuli behind it in H. medicinalis ; but the female orifice may 

 vary with regard to the male in other genera. A number of nephridial 

 orifices can be seen as paired openings on the posterior annuli of many of the 

 somites. Eyes exist as small, dark dots on the dorsum of the body, behind 

 the anterior sucker. The mouth may be armed or unarmed. In the former 

 condition it possesses three jaws — one dorsal and two ventro-lateral — each 

 with a thickened free edge notched with teeth. In the latter there may be 

 only a proboscis. Into the mouth open the salivary glands, which secrete a 

 fluid which prevents the coagulation of the blood. The pharynx is an oval 

 sac, with strong muscular walls and radial muscles, which can alternately 

 contract and dilate the cavity, thus forming a sucking-pump. From the 

 pharynx an oesophagus leads to the crop, which is a straight, thin-walled tube 

 with lateral diverticula. 



Behind the crop comes the small stomach, which opens into a narrow 

 straight tube — the intestine — which runs to the anus. The coelom consists 

 of a series of tubes containing red blood. The excretory system consists of 

 the nephridia. There is a supra-cesophageal ganglion, a nerve collar, and a 

 ventral nerve chain. The male reproductive organs are a number of testes, 

 with yasa efierentia opening into two vasa deferentia, which, after coiling 

 into epididymes, run to the single penis. The female organs are a pair of 

 oveiries and oviducts opening into a single vagina. 



Biology — ^Leeches appear to be essentially water animals, and 

 though certain genera can live on land, still, they require a great 

 deal of moisture. Hence land leeches retire into moist places under 

 stones, earth, etc., and only come out when requiring food. In 

 dry weather not a leech can be seen, while in damp weather they 

 may be very abundant. 



Any disturbance of the air appears to affect them. Hence they 

 are quickly aroused from their retreats when a human being or 

 animal approaches, and set forth at once, often with considerable 

 speed, to the attack. 



The bite is not always painful at first, and may not be noted 

 until the flow of blood is observed. The leech, while biting, keeps 

 itself and the skin of the victim moist by liquid excreted by the 



