NAIS. 129 



CHAPTER IV. 



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NAIS. LUMBRICUS. 



NATURALISTS 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, single 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 I am much surprised to see some of those naturalists who offer their 

 works to the world, overlook the embarrassments obstructing the true 



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