HIRUDO. 21 



the head having been again introduced, and also withdrawn several 

 times, the capsule was in some minutes fashioned into a broad ovoid, the 

 embryonic specks being shifted about by the pressure of its parts, while 

 the leech seemed occupied in diffusing it on the glass, and after promot- 

 ing its adhesion, it was forsaken. 



Now the capsule was nearly transparent, exposing five white specks 

 towards the centre. It underwent scarcely any change in an hour. With 

 the lapse of five hours it had acquired the fine brownish colour of others. 



It is evident, therefore, that the capsule is originally a film formed 

 around the body of the leech, and through which a portion of the an- 

 terior, comprehending the orifice of the oviduct, passes. Farther, that 

 it receives the embryonic specks directly from the oviduct itself; but 

 whether in fluid matter, or in a common involucrum, or separately, is 

 uncertain. 



There are only two obvious modes whereby the capsule can be pro- 

 duced ; first, as an entire sac ; second, as an exudation, like the protecting 

 silk, or sheath so often quoted, from the surface of the skin. 



The capsule is always pellucid originally, and great irregularity 

 always subsists in the number, the position, and the progressive evolu- 

 tion of the embryos. 



In the years 1803 and 1812 a leech occurred to me in the parish of 

 Abercorn, which I was induced to consider a variety of the octo-ocidata. 

 Having no opportunity of afterwards revisiting the spot, which was a 

 small marsh, I directed a quantity of its contents to be transmitted in a 

 pitcher, being then fifteen miles distant, expecting to find some of the 

 subjects resembling those previously obtained. 



I was not disappointed ; they confirmed my earlier observations, in 

 as far as denoting that they had been made on a slight variety of the 

 Hirudo octo-oculata or vttlgaris. 



This variety rather exceeds the dimensions of ordinary specimens. 

 It is of a fine, smooth, uniform colour, of delicate aspect. The body, 

 consisting of numerous segments, is wholly environed by a broader, 

 clearer, and more distinct margin than the other. No speckling, mottling, 

 or reticulation distinguishes the surface. But there is some irregu- 



