igo WOUMS. 



will be seen to move by alternately fixing and loosening its 

 oral and posterior suckers, while some slight provocation, 

 such as some drops of chloroform or alcohol, will induce 

 the animal to swim about both actively and gracefully. 

 The animal will also be seen to cast off frorn its skin thm 

 transparent shreds of cuticle, — a process which, in natural 

 conditions, usually occurs after a heavy meal, when the 

 animal as if in indigestion spasmodically contracts its body, 

 or rubs itself on the stems of water-plants. As we shall 

 afterwards see, numerous eggs are laid together in cocoons 

 deposited in damp earth near the edge of the pool. Thence 

 after a direct development, young leeches emerge and make 

 for the water. 



External Features. — The leech usually measures from 

 two to six inches in length, and appears cylindrical or 

 strap-hke according to its state of contraction. The slimy 

 body shows over a hundred skin-rings ; the dorsal sur- 

 face is beautifully coloured with distinct rows of spots in 

 contrast to the irregularly mottled under-side ; the suctorial 

 mouth is readily distinguished from the unperforated hind 

 sucker, above which on the dorsal surface the alimentary 

 canal may be seen to end. More careful examination shows 

 five pairs of little black " eyes " distributed on the first eight 

 rings of the head, the swollen protrusion of the male organs 

 which open on the middle ventral line between rings 30 

 and 31, a similar aperture of the female organs five rings 

 further back, seventeen small openings down each side of the 

 ventral surface through which a whitish fluid may be 

 squeezed — the apertures of the excreting organs. The 

 skin-rings, of which there are 102 in all, are superficial 

 wrinkles, disguising the true body-segments, which are deter- 

 mined by the internal arrangements of nerve-centres and 

 excretory tubes. The true segments are 26 in number, 

 and this fact may be recognised even externally, since 26 of 

 the 102 skin-rings are distinguished from their neighbours 

 by the possession of numerous " sensory spots." The 

 number of sensory rings is thus equal to the number of true 

 segments. There are usually five skin-rings to each seg- 

 ment, but fewer at each end. In illustration, we may 

 pote that the male aperture between rings 30 and 31 is on 

 the tenth segment, and the female aperture between 35 and 



