NAIS. 129 
CHAPTER IV. 
NAIS—LUMBRICUS. 
Naturauists have frequently chosen very delicate features for the 
purpose of dividing the different tribes of animals into groups ; such, too, 
as are often difficult to recognise, and not, perhaps, the most obvious 
actually existing. For this selection there are as yet no positive rules 
laid down, and sometimes, therefore, very equivocal principles are adopt- 
ed. In proportion to the minuteness of the subject, and the complexity 
of organization, the uncertainty is augmented. But unexpected trans- 
parence, and microscopic aid, occasionally render that structure explicit 
which it would be fruitless to search after by ordinary methods. 
§ 1. A distinction has been attempted of worms into smooth and 
hispid, and a genus constituted out of the latter, denominated Nais. But 
there are many of the Vermes whose precise formation is of such difficult 
observation, that we are actually puzzled to discover whether they are 
hispid or not. 
By hispid, I understand that the body is characterised by hairs or 
bristles, smgle or fasciculated on the surface, or which may be protruded 
so as to project above the skin. 
This subject has none of the facilities which attend many others ; 
and J am much surprised to see some of those naturalists who offer their 
works to the world, overlook the embarrassments obstructing the true 
R 
