24 



OUTLINES OF NATURAL HISTORY. 



worms, and Sand-worms, and derive their name from the 

 fact that the integument or skin is markedly ringed or 

 thrown into transverse folds (Latin, annuhis, a ring). As 

 an example of this class, we may select the Common 

 Medicinal Leech {Sanguisuga officinalis). 



The Leech (fig. lo, a) is of an elongated, cylindrical, 

 worm-like form, tapering towards its head, but capable of 



greatly contracting or lengthening 

 itself at will. Its skin is quite 

 soft and flexible, slimy to the 

 touch, and very markedly ringed 

 or transversely folded, the total 

 number of rings being about one 

 hundred. At each extremity of 

 the body it shows a little sucking 

 disc or cup (fig. ii, B, as and^j)*), 

 by means of which it can move 

 actively about. The hinder sucker 

 (ps) is distinctly constricted off" 

 from the body by a kind of neck, 

 is not perforated by any aperture, 

 and is provided with an even cir- 

 cular margin. The front sucker 

 is of an elongated form (as), is 

 really formed mainly out of the 

 „, „ , elongated upper lip, and is per- 



Fig. lo. — a The Medicinal j-„^„f„,i k , +1, • « ai. 



Leech (Sanc/aisuga offici- lorated by the opening of the 

 naiis), natural size ; 6 An- niouth. When movinff, the Leech 



tenor extremity of the same n -i. t • ^ ^ ■, 



magnified, showing the "xes its hinder sucker, and 

 Slicker and triradiate jaws ; stretches out its head till it meets 



c One of the jaws detached, .,, i- i n • • i 



showing the semicircular Wltn SOme SOlld object ; it then 



toothed margin. detaches the hinder sucker, and 



brings this forward till it adheres close beside the spot 

 where the head has fixed itself. Then, detaching the 

 head, it again extends itself to seek another point of at- 

 tachment further on. By a repetition of this process, 

 the Leech can travel with considerable rapidity; but it 

 also swims well by a serpentine bending of the body. 



The body of the Leech is absolutely destitute of limbs 



