136 ZOOPHYTES. 



Common features must regulate the constitution of genera ; and the 

 profound naturalist, when completely master of the form and the facts, 

 will select such as are sufficiently prominent to sanction the arrangement 

 of a Sijstema Naturee. 



In aid of this desirable object, I have endeavoured to point out some 

 peculiarities in the living products already discussed, as seemed more in- 

 teresting, and the least liable to be mistaken. I shall still continue a 

 similar course ; — yet, without affirming that, spite of all the care bestowed 

 on them, various essential characters have not been overlooked, or that I 

 have not erred in respect to some which should be corrected. 



There is no doubt that sufficient distinctions subsist among the ani- 

 mated tribes, to warrant the association of few or of many in certain sec- 

 tions, and thus to facilitate the prosecution of science. 



It is from the conviction of some principles being hastily and inap- 

 propriately adopted, that the names deduced from them are not more ap- 

 plied throughout these pages. Also, I consider it, meantime, better to 

 retain names already recognised, though not strictly appropriate, than to 

 disturb their application by interference. 



If we confine the Scotish Tuhularice to zoophytes, " with a fistulous 

 stem, bearing a hydra which has two separate rows of tentacula, and ova- 

 rian clusters interposed between them," positive features of easy recogni- 

 tion define the genus, wherein the species comprehended are very few. 



Were the name of Sertularia retained in its original sense, " a plantula 

 or little plant," — merely a diminutive, it would comprehend the great ma- 

 jority of those denominated flexible zoophytes. 



I feel disposed to claim it occasionally as a useful and convenient 

 auxiliary, for which no adequate substitute has been hitherto suggested. 

 Our progenitors preferred brief and explicit definitions from clear and de- 

 cisive features. They did not deal in many words. 



Nothing can be more appropriate for common use than the definition 

 in question, as in the Sy sterna — " an animal growing in the form of a plant : 

 Stem branched, producing polyjn from cup-shaped denticles or minute 

 cells." Further, the genus was divided into two portions ; one with a 

 horny stem, and fiirnished with ovarian vesicles ; the other having a a-us- 



