HIRUDO. 3 



sucker in front is relieved, carried forward, and secured, when the pos- 

 terior is relieved, carried forward, and secured in like manner, whereby 

 the animal has taken its step. This process is repeated, while adhesion 

 constantly prevails. The Leech also swims quickly by undulations in the 

 water. It feeds on animal and vegetable substances ; and it multiplies 

 by means of ova. 



1. HIRUDO MURICATA The Skate Leech. Plate I. fig. 1. 



Length eight inches ; extreme diameter seven lines. Body round, 

 tapering slightly from the middle towards the two extremities, each of 

 which dilates as a large circular sucker. The whole body profusely 

 tuberculated ; the tubercles rising about a line, disposed in regular circles, 

 and susceptible of being flattened. A portion of the neck near the head 

 differs somewhat from the rest, in forming a broad belt of lower tubercles. 

 Neither eyes nor ocular specks are to be discovered. 



The body is annulated, as may be discovered from young specimens, 

 for this becomes imperceptible with their growth. Between seventy and 

 eighty distinct circles were enumerated in one extending about two 

 inches hi length, by a line in thickness, the tubercles seeming to be ar- 

 ranged in about eight longitudinal rows. 



During quiescence the animal adheres firmly by the posterior sucker ; 

 it forms in its extent a logarithmic curve, with the oral disc expanded 

 or otherwise in the centre. Now the disc appears as a hollow hemi- 

 sphere, which unfolds as a flattened surface, to be applied to neighbouring 

 objects when the animal commences its progression. While altogether 

 disengaged, the lip of the hemisphere contracts so as to render it spheri- 

 cal. When employed, it is unfolded flat ; the mouth appearing in the 

 centre, environed by concentric rings of different lines. The exterior 

 ring was in one specimen greenish, the next white, very narrow, within 

 a broad grey ring. Eight low tubercular prominences are disposed on the 

 margin of this oral sucker ; sometimes four, as were on the disc just 

 described. There is a considerable contraction of the diameter of the 



