LEECHES. 



87 



Fig. 76. 



LEECH. 



and divided into a great many segments : it is 

 entirely without legs or setce, but has at either 

 extremity, a dilatable, prehensile cavity, which 

 performs the functions of a cupping-glass. 

 The mouth, situated at the bottom of the anterior 

 or oral sucker (fig- 76, a), has neither trunk 

 nor tentacle, but is armed with hard parts which 

 serve the purposes of jaws. It has a certain 

 number of eyes, or rather ocellar points, situated 

 on the dorsal face of the anterior extremity of 

 the body. The anus is placed at the bottom of 

 the posterior sucker (b). 



13. All these anne'lides feed at the expense of 

 other animals. They attach themselves to fishes 

 or batrachians; sometimes they devour mollusks, 

 anne'lidans, or the larvae of insects; certain 

 species attach themselves to horses and cattle, 

 and even to men, when they drink at springs; 

 sometimes fixing themselves under the tongue, in 

 the nostrils, or even in the gullet. 



The mouth of a leech is an exceedingly perfect appara- 

 tus. u Around the entrance of the oesophagus are disposed 

 three minute cartilaginous teeth, imbedded in a strong cir- 

 cle of muscular fibres. Each tooth has somewhat of a semi- 

 circular form, and, when accurately examined with a 

 microscope, is found to have its free margin surmounted 

 with minute denticulations so as to resemble a small 

 semicircular saw (fig. 77). On watching a leech atten- 

 tively during the process of biting, the action of these 

 teeth is at once evident ; for, as the skin to which the 

 sucker is adherent is rendered quite tense, the sharp 

 serrated edges of the teeth are pressed firmly against it 

 and, a sawing movement being given to each cartilagi 

 nous piece by the strong contractions of the 

 muscular fibres around the neck, these in- 

 struments soon pierce the cutis to a consider- 

 able depth, and lay open the cutaneous ves- 

 sels, from which the creature sucks the fluid 

 which its instinct prompts it to seek after 

 with so much voracity. The position of the 

 teeth around the opening of the mouth, as 

 represented in the annexed figure (78), will 

 at once explain the cause of the tri-radiate 

 form of the incision which a leech-bite in- 

 variably exhibits." T. Rymer Jones. 



The use of leeches is so general in 

 the practice of medicine, that they 

 ^aave become an important object in 

 commerce. They are imported from 

 Spain, Portugal, and other countries 



Fig. 77. 



TOOTH OF A IJSECH 



Fig. 78. 

 HEAD OF A LEECH MAGNIFIED 



13. What are the habits of sucking Anne'lidans ? 



