SANGUISUGA. 



so that the oval aperture is firmly applied to any surface upon 

 which this part of the animal is fixed. Around the entrance 

 of the oesophagus are disposed three minute cartilaginous 

 teeth, imbedded in a strong circle of muscular fibres. Each 

 tooth has somewhat of a semicircular form, and when accu- 

 rately examined with a microscope, is found to have its free 

 margin surmounted with minute denticulations, so as to 

 resemble a small semicircular saw. On watching a leech 

 attentively during the process of biting, the action of these 

 teeth is a-t 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 cartilaginous piece by the strong contrac- 

 tions of the muscular fibres around the neck, these instru- 

 ments soon pierce the cutis to a considerable depth, and lay 

 open the cutaneous vessels, 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 will at once explain the cause of the tri-radiate 

 form of the incision which a leech-bite invariably and con- 

 stantly exhibits. 



On contemplating this singular dental apparatus found in 

 the medicinal leech, and considering the nature of the food 

 upon which it usually lives, it is difficult to avoid arriving at 

 the conclusion that such a structure, which is indeed only 

 met in one or two species, is rather a provision intended to 

 render these creatures subservient to the alleviation of human 

 suffering, than necessary to supply the wants of the animals 

 themselves. In the streams and ponds which they usually 

 inhabit, any opportunity of meeting with a supply of the 

 blood of warm-blooded Vertebrata must be of rare occurrence, 

 so that comparatively few are ever enabled to indulge the 

 instinct which prompts them to gorge themselves so vora- 

 ciously when allowed to obtain it ; neither does it appear that 

 the blood which they swallow with so much avidity is a ma- 

 terial properly suited to afford them nourishment ; for although 

 it is certainly true that it will remain for a considerable time 

 in its stomach without becoming putrid, yet it is well known 

 that most frequently the death of the leech is caused by such 

 inordinate repletion, provided the greater portion of what is 

 taken into the body is not speedily regurgitated through the 

 mouth. 



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