LEECHES OF COMMERCE. 217 



it wishes to surround. In the centre of trie mouth- 

 sucker are three small but sharp teeth, and near the 

 anterior margin (in the medicinal leech) are ten very 

 small black eyes, arranged in the form of a crescent. 

 At the bottom of the mouth-sucker begins the digestive 

 tube of leeches. Those frequently used in medicine, 

 and so greedy of human blood, easily pierce the skin by 

 means of their teeth. A recent communication to the 

 Societe Zoologique d'Acclimatation makes known the 

 existence in America of leeches possessing this valuable 

 peculiarity, that they leave no mark on the skin to 

 which they are applied, so that they must act not by 

 biting but by suction. This curious fact is put beyond 

 a doubt by the experiments made upon himself by Cra- 

 veri, a learned Italian. M. du Filippi has placed these 

 leeches in a new genus, which he terms Hcementaria, 

 and of which he describes three species, two belonging 

 to Mexico, and one to the river Amazon. The blood 

 which they suck passes abundantly into the oesophagus 

 and the stomach, which is remarkable for its size in 

 comparison with that of the body. 



The leeches of commerce are the green (Hirudo cffi- 

 cinalis) and the grey (Hirudo medicinalis). Each of 

 these species presents several varieties, of different 

 degrees of utility, and thus inviting unscrupulous ven- 

 ders to practise their tricks of trade. A good leech is 

 long and flat. The outer skin is of a particular velvety 

 appearance. It moves in water with great activity, 

 and stretches itself out remarkably. Its elasticity is 

 such that it can treble its length, and twine round the 

 finger like a ribbon. The fineness of the anterior com- 

 pared with the posterior part of its body is also a sign 

 of good quality. Fraudulent dealers mix the different 

 kinds, or gorge them with blood in the proportion of 45 

 or 50 to the 100, in order to make them weigh more, 

 leeches being sold by weight ; so that small leeches, 

 worth 75 francs, are sold for 130. This fraud may be 

 thus detected : The leech, designedly gorged, has a 



