FORMS OF THE POLYPIDOMS. 53 



and some other naturalists. It rests on the assumption that the 

 polypidom is extravascuhir and inorganic, so that after its first 

 sohdification, it suffers no aUeration in form and quahty, beyond 

 what is evidently effected by the operation of chemical and me- 

 chanical causes : the changes resulting from its increase in size, 

 are not from the activity and pulsion of any inherent principle, 

 but from the super-imposition of additional layers, or from the 

 additions of new cells, or from the prolongation of the tubes, 

 which additions are all coetaneous with the growth and multi- 

 plication of the polypes, and the results of new secretions. Lin- 

 nceus, Pallas and Baster opposed Ellis, and believed in a vege- 

 tative principle, inherent in the polypidom itself, so that its growth 

 was in some measure independent of the living tenant ; and va- 

 rious arguments have been brought forward by Bory de St Vin- 

 cent,* which appear to him to demonstrate the truth of this 

 doctrine. We may act, however, not unreasonably in withhold- 

 ing our assent, for with such a feeble and errant point was the 

 argument handled that few felt its force, and the discussion has 

 continued even to this day in an unsettled state. It seems pro- 

 bable in fact that neither theory will explain the growth of all 

 polypidoms ; and as the peculiarities which distinguish these are 

 considerable and would render a general description involved and 

 obscure, I shall reserve the explanation of their mode of increase 

 for a section in the preface to each separate order. Enough 

 has in the meantime been said to show how unimportant the 

 polypidom must be as a primarij character in a natural classifi- 

 cation of zoophytes, and yet, until very recently, no other basis 

 was looked for or deemed available, and hence the artiiicialness 

 of the proposed " Systems" which, as a matter of history, we 

 now venture to review. 



The Classifications of Zoophytes. 

 The main object of Ellis being to prove the animality of zoo- 

 phytes, he deemed a new classification of them unnecessary, and, 

 as it was sufficient for his purpose, he followed very closely that 

 which had been proposed by Ray in his Synopsisof British Plants, f 

 In successive chapters he treats of the vesiculated corallines 

 { Sertulariadse), the tubular corallines (Tubularise), of the cel- 



• Encyclop. Method, art. Zoophyte. 



t Syii. Meth. Stirpium Brit. Edit. 3. Load. M'lA. 



