ANATOMY OF THE LEECH. 



219 



Dental apparatus of the Leech. A., triradiate arrange- 

 ment of the teeth or saws ; B, a tooth magnified. 



the cause of the triradiate form of the incision that a leech-bite in- 

 variably exhibits. 



(574.) On contemplating this singular dental apparatus found in the 

 medicinal Leech, and con- 

 sidering the nature of the Flg> 106 ' 

 food upon which it usu- 

 ally lives, it is difficult to 

 avoid arriving at the con- 

 clusion that such a struc- 

 ture 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 

 where they usually in- 

 habit, 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 in- 

 dulge the instinct that prompts them to gorge themselves so voraciously 

 when allowed to obtain it : neither does it appear that the blood which 

 they swallow with so much avidity is a material 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. 



(575.) The internal digestive apparatus is evidently adapted, from the 

 construction of all its parts, to form a capacious reservoir for the recep- 

 tion of fluids taken in by suction : the stomach, indeed, with the nume- 

 rous lateral appendages opening from it on each side, would seem to fill 

 the whole body ; and, being extremely dilatable, allows the animal to 

 distend itself to a wonderful extent, so that it is not unusual to see a 

 leech, when filled with blood, expanded to five or six times the dimensions 

 natural to it in an empty state. 



(576.) The stomach itself (fig. 107, h, i) occupies about two-thirds of 

 the visceral cavity ; on opening it, as represented in the figure, it is 

 seen to be divided by delicate septa into nine or ten compartments that 

 communicate freely with each other. In each compartment we observe 

 two lateral orifices leading into as many wide membranous pouches (&), 

 which, although shrunk and flaccid when in an undistended condition, 

 as they are seen in the figure, are easily filled with fluid introduced into 

 the stomach, and are then swelled out into very capacious bags. Perhaps 



