HI RU DINE A 



685 



nephridia and the dermal glands. When it has gorged itself with 

 blood it drops off, but its salivary secretion prevents the coagulation 

 of the blood, and hence the site of the leech-bite bleeds considerably 

 for some time. The blood is stored up in the crop and its caecal 

 diverticula, and only a little is used day by day for food. 



Pathogenicity.— Leeches are hosts of trypanosomes and other 

 parasites, and their bite may possibly introduce these parasites 

 into the skin of the human victim as well as into that of animals. 



The marked feature of the pathogenesis is loss of blood, not 

 merely caused by the sucking of the leech, but also by the bleeding 

 from the wound caused by the bite. Further, the punctures 

 caused by Hcemadipsa zeylanica are extremely liable to become 

 ulcers, which, according to Marshall and Davy, caused a high rate 

 of mortality among the Madras sepoys and coolies during the 

 Kandyan rebellion of 181 8 in Ceylon. Short of death, amputa- 

 tion of the limb was necessary in those days. We are not inclined 

 to consider these old statements as erroneous, because it is quite 

 possible that some organism is often introduced into the affected 

 part by the leech-bite. For a further discussion of the pathogeni- 

 city, see the chapters on Diseases of the Respiratory Organs and 

 of the Skin. 



Classification. — The class Hirudinea may be divided into several orders: — 

 Order I.: Rhynchobdellida. — Hirudinea without jaws, with an extensile pro- 

 boscis and with colourless blood, living in salt and fresh water. 

 The Rhynchobdellida are divided into two families : 



Family i : Ichthyohdellidcs. — Rhynchobdellida with the anterior narrower 

 part of the body distinct from the posterior, and with both suckers distinct 

 from the body. 



To this family belong the genera Pisciola de Blainville, 181 8, and Pontobdella 

 Leach, 181 5, mentioned in the chapter on Protozoa. 



Family 2: GlossiphoniidcB . — Rhynchobdella with the anterior sucker fused 

 to the body, while the posterior is distinct. 



Among the genera of this family is Hcsmentaria de Filippi, 1849, of which 

 H. officinalis de Filippi is found in Mexico, and is alleged to cause drowsiness, 

 buzzing in the ears, and a painful rash, when it bites a person. The causation 

 of these symptoms is obscure. Another species is H. ghiilanii de Filippi, 1849. 



Other genera are Glossiphonia Johnson, 1816; Hemiclepsis Vejdovsky, 1883; 

 and Placohdella R. Blanchard, 1893. 



Order II. : Arhynchohdellida. — Hirudinea usually with jaws, without a 

 proboscis, and with red blood, living in fresh water or on land. There are 

 two families, Gnathobdellidae and Herpobdellidae, of which only the first 

 concerns us. 



Family Gnathobdellidae. 



Arhynchobdellidge with five or more, rarely four, pairs of eyes, and, except 

 in the Semiscolinae, with three denticulate jaws. Eggs enclosed in a spongy 

 cocoon, which is deposited above water-line. 



The Gnathobdellidae are classified into the following subfamilies: Hirudi- 

 ninge, Haemadipsinse, and Semiscolecinae, which last is not of interest to us. 



Subfamily HiRUDiNiNiE R. Blanchard, 1894. 



Aquatic Gnathobdellidae with ten eyes, and with an eyeless ring between 

 the third and fourth pair of eyes, with denticulate jaws. Complete somite 

 iqxv^ed of five rings. The nephridial pores open near the margins of the body 

 on the ventral surface. 



