SANGUISUGA. 



of the animal depend, but the cutis or true skin is so inti- 

 mately connected with the muscular integument of the body, 

 that its existence as a distinct tunic is scarcely demonstrable. 

 The muscular covering or walls of the body, which form a 

 kind of contractile bag inclosing the viscera, are found upon 

 accurate dissection to consist of three distinct strata of fibres 

 running in different directions. The outer layer is composed 

 of circular bands, passing transversely ; in the second the fibres 

 assume a spiral arrangement, decussating each other, while 

 the internal layer is made up of longitudinal muscles extend- 

 ing from one end of the creature towards the opposite. Such 

 an arrangment is evidently adequate to the production of all 

 needful movements, and capable of giving rise to all the mo- 

 tions 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 ; never- 

 theless, 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 accom- 

 plished by means of the terminal suckers, supposing the pos- 

 terior 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 

 contractions of the muscular integument, not precisely under- 

 stood, 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. 



The mouth of the leech is an exceedingly perfect appara- 

 tus, not only adapted 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, 



3 



