82 Snail-Leeches. 



which specimens inay be obtained renders continuous investi- 

 gations easy. 



The snail-leeches are properly separated from the true red- 

 blooded leeches, such as Hirudo medicinalis, Hcemopis sanguis 

 suga (horse-leech), Nephelis (whose oval capsules with, their 

 contained eggs are common at this time of the year on every 

 aquatic plant), Trochetia and Aulastmna, which form the family 

 of Hirudinacea (see Grube's Die Familien der Anneliden, 

 Berlin, 1851). The snail-leeches, which have colourless blood, 

 and differ in several important particulars from the true leeches, 

 form, with the genus Piscicola,* a distinct family, to which, from 

 their possessing a peculiar characteristic proboscis capable of 

 exsertion, the appropriate name of Glossiphonidce (syphon- 

 tongued) was proposed by Dr. E-awlins Johnson in 1816. 

 Before the researches of Dr. E,. Johnson, the Glossiphons were 

 classed promiscuously with various other leech-like animals, to 

 which the generic name of Hirudo was given. This appropriate 

 term has been unfortunately allowed to give place to that of 

 Clef sine, proposed, I believe, by Savigny in 1827. What the 

 derivation of the word may be I am unable to discover. 



The snail-leeches inhabit fresh water, and no marine species 

 have as yet been found. In every brook, in every pond, and 

 almost in every ditch, certain species occur. As a rule pure 

 water is preferred, but Qlossiphonia bioculata and G. hyalina 

 are by no means particular in this respect. The normal form 

 of a snail-leech when at rest may be described as follows : — 

 Body dilated and depressed; upper surface more or less convex ; 

 the under surface is flat and concave ; the anterior extremity, 

 which in a few species may be said to form a distinct head, is 

 always less obtuse than the anterior; the mouth, which is 

 situated nearly at the apex of the anterior extremity, is trans- 

 versely elliptical, two-lipped., and furnished with a strong mus- 

 cular protractile proboscis ; eyes variable, according to the 

 species, there being either one, two, three, or four pairs, gene- 

 rally of a black or deep claret colour, disposed in two longi- 

 tudinal series, but slightly converging towards the anterior 

 extremity ; in some individuals the anterior pair are wanting, 

 and the order of arrangement is confused. The hind sucker is al- 

 ways much larger than the front one; indeed, the mouth, forming 

 the anterior sucker or acetabulum, is no true sucker at all.f The 

 colour of the different species, as well as the consistency of the 

 body, varies ; some are grey with rows of dull spots, others 

 minutely speckled, others marked with golden dots; some are 



* I include Piscicola with the G-lossiphons on the authority of Grube, who 

 recognizes a proboscis in that genus, but I am not satisfied that Piscicola is pos- 

 sessed of this organ. 



f Piscicola, however, has the anterior sucker fully developed. 



