CLASSIFICATION 405 



close up when it is free from the body ; it is then whitish and 

 soft, and the leech fixes it, and appears to polish the surface with 

 its buccal sucker. In a few hours the cocoon becomes amber 

 brown, a colour which characterises the cocoons of a great many 

 earthworms and other Oligochaeta. The medicinal leech forms 

 its cocoon in the same way as does Nephdis, to which the above 

 description refers; but when the cocoon is formed the leech 

 covers it with another layer of mucus, which Vaillant, from 

 whose work the foregoing notes are extracted, 1 thinks may be 

 produced from the so-called salivary glands. 



Classification. The number of different kinds of leeches 

 is at present uncertain. Seeing that no less than sixty-four 

 varieties of the common Hirudo medicinalis colour varieties, it is 

 true are said to exist, it is not wonderful that the labours of 

 some systematists have been severe, and have provoked much 

 criticism and alteration on the part of others. 2 As to genera, 

 Vaillant, in his recent continuation of de Quatrefages' " Anneles " 

 in the Suites ti Buffon, which includes the literature up to the 

 year 1886, allows thirty-seven, some (three) of which, however, 

 are admitted to be incertae sedis. Blanchard, who has paid a 

 great deal of attention to the group, reduces these by six, which 

 he considers to be synonyms ; but on the other hand he has 

 added or rescued from oblivion six or seven others, and Whitman 

 has instituted several Japanese and Australian genera. Most of 

 these generic types are, however, only imperfectly known, and 

 from external characters only. It is quite problematical how 

 many valid genera should be retained ; in the meantime those 

 that are fairly well known are divided by Blanchard s in the 

 following way : 



Sub-Order 1. Rhynchobdellae. Hirudinea with an exsertile 

 proboscis, without jaws, and with colourless blood. 



1 "Anneles," vol. iii. 1889-90, p. 493, in the Suites A Buffon. 



2 Whitman quotes with regretful approval (Proc. Amcric. Acad. xx. 1884-85, p. 76) 

 Sir J. Dalyell's remark, ' ' It does not appear that the history of the leech has advanced 

 in proportion to the number of literati who have rendered it the subject of dis- 

 cussion," and adds on his own account the following severe indictment of his 

 predecessors : "As a considerable share of the work done in this direction 'is 

 purely systematic, it is somewhat surprising that not a single description of any 

 Hirudo lias been given with sufficient accuracy and completeness for a close com- 

 parison of even its more important external characters with those of other species." 



3 " Hirudinees de 1'Italie," etc. , Boll. Mus. Zool. Torino, vol. ix. 1894, No. 192. See 

 also Apathy, "Siisswasser-Hirudineen," Zool. Jahrb. Syst. iii. 1888, p. 725. 



