192 ANNELIDA. 



muscles, extending from one end of the creature towards the oppo- 

 site. Such an arrangement is evidently adequate to the produc- 

 tion of all needful movements, and capable of giving rise to all 

 the motions connected with the elongation, contraction, or lateral 

 inflexions of the body used in progression. 



At each extremity of the animal, the muscular coat expands into 

 a flattened fleshy disc, composed of circular and radiating fasciculi, 

 which, when applied to a smooth surface, perform the office of 

 suckers, and thus become important instruments of prehension. 

 There are no vestiges of external limbs ; nevertheless, with the 

 simple mechanism above described, the leech is able to crawl with 

 considerable rapidity along the surface of subaquatic plants, or even 

 to swim with much facility through the water. The first method 

 of locomotion is accomplished by means of the terminal suckers : 

 supposing the posterior disc to be attached, the animal elongates 

 its body to the utmost, and then fixes the sucker placed at the 

 opposite extremity ; this done, the hinder parts are drawn forward 

 and again fixed, preparatory to a repetition of the process. In 

 swimming, the whole body is elongated, and by some partial con- 

 tractions of the muscular integument, not precisely understood, 

 assumes the appearance of a flattened band, and in this condition 

 the leech makes its way through the element which it inhabits, 

 by successive undulatory movements of the body performed with 

 much grace and elegance. 



(235.) The mouth of the leech is an exceedingly perfect appa- 

 ratus, adapted not only to the destruction of those minute aquatic 

 animals which constitute its usual food, but, as is universally 

 known, admirably fitted to extract blood from the higher animals ; 

 combining, in its operation, the offices both of the cupping-glass 

 and the scarificator. 



The mouth is situated near the centre of the anterior sucker, so 

 that the oral 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, im- 

 bedded in a strong circle of muscular fibres (fig. 79, 1). Each 

 tooth has somewhat of a semicircular form, and, when accurately 

 examined with a microscope, is found to have its free margin sur- 

 mounted with minute denticulations (fig. 79, 2), so as to resem- 

 ble a small semicircular saw. On watching a leech attentively 

 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 



