2 HIRUDO. 
genus Hirudo, which cannot but be interesting to the physiologist, and 
assuredly deserve to be farther known and suitably appreciated. 
I might have been deterred from offering farther observations on 
this, a very interesting subject in Natural History, considering the 
valuable treatises already published by such distinguished authors as Dr 
James Rawlins Johnson, Professor Stefano Delle Chiaje of Naples, M. 
Moquin Tandon of Montpellier, and many others, wherein a historical 
and descriptive view of the whole is taken, especially by the last. But 
certain species, both marine and fresh-water, have occurred to me, which 
seem rarely distributed. Besides, my endeavours to preserve all animals 
alive, afford opportunities of presenting several new facts in the history 
of some, and accurate representations of the form of others. 
There is nothing in the whole circle of literature which has hitherto 
experienced so total a failure as the last. I cannot specify a single 
treatise containing even tolerable figures of the Leech ; and although 
very familiar with various species named by different authors, it is very 
rarely that I have derived any assistance from the figures offered in 
illustration, or have been able to identify them with my own. This 
defect, however, must be ascribed equally to the imperfection of the 
creature, which is not selected while vigorous, and to the deficiencies of 
the artist. 
Many doubts have been expressed regarding the just position of the 
Leech in the Systema Natura, and sometimes by those who apparently 
question whether there is any specific order or arrangement of things 
manifested by the Creation. Yet the tribe of leeches is, if I may so ex- 
press it, absolutely saz generis; none other has been hitherto shewn in 
close approximation. It seems to stand apart. At present it is brought 
nearer to the simple Vermes than either its general formation or its 
general habits sanction. But there being many reputable works, which 
T have not been able to procure, on the subject, probably they contain 
sufficient illustrations. 
The Leech is a soft bodied, elongated, annulose animal, of the most 
variable form. Both extremities dilate, in each constituting a sucker, 
affixing it firmly to any foreign substance. It cannot advance unless the 
