HIRUDO. 43 



and unconstrained operation of the vital functions. Their play is with- 

 out violence to the living being, or the suffering inseparable from artifi- 

 cial exposure of the parts. Neither convulsions, contraction, nor irrita- 

 tion impair or impede the due exercise of the peculiar functions pertain- 

 ing to the respective organs. 



But this is an advantage to be very seldom gained. We have just 

 witnessed some approximations to it, which, in this particular race of 

 animals, can be scarcely carried farther. 



The peculiar form of the head, the number or arrangement of the 

 eyes, and the consistence of the body, distinguish the preceding species. 

 That which is before us is not quite so strongly marked, but it evidently 

 belongs to the same division of the genus Hirudo. 



I regret, however, that only a single adult specimen has come into 

 my possession, discovered by the same affectionate relative, the com- 

 panion of all my excursions and researches, as noted, when speaking of 

 the Cristatclla in a previous treatise. 



The deficiency of adults, however, has been fortunately in a great 

 measure compensated by a profusion of the young ; affording still ano- 

 ther example of the benefit that may be eventually derived from preser- 

 vation of a single specimen. 



The subject in question extends above two inches, tapering slightly 

 from near the sucker, where it is between two and three lines in breadth. 

 The head is lanceolate, with four pair of black eyes, in the middle of the 

 surface, disposed much as in the Chequered Leech, but the animal not 

 being in as favourable a position, a less distinct view has been obtained. 

 The body is divided into numerous narrow segments, so numerous, that at 

 first sight I supposed it a small specimen of the sanguisuga or Horse Leech. 

 The colour is universally dark green, and its appearance much of the 

 character exposed on the fracture of a common dark green bottle. The 

 surface is faintly speckled under the microscope ; and the belly somewhat 

 paler. Like the tesscllata, the substance is tremulous, though to a slighter 

 degree than in that animal. Plate V. fig. 20, Hirudo vitrina, back ; 22, 

 belly ; 21, head irregularly contracted ; 23, young specimen. 



