438 FORMS OF THE POLYPIDOMS. 





the polypes, and this opinion has been maintained recently 

 by Lamarck, and some other naturalists. It rests on the 

 assumption that the polypidom is extravascular and inorganic, 

 so that after its first solidification, it suffers no alteration in 

 form and quality, beyond what is evidently effected by the 

 operation of chemical and mechanical 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 multiplication of the 

 polypes, and the results of new secretions. Linnaeus, Pallas 

 and Baster opposed Ellis, and believed in a vegetative prin- 

 ciple, inherent in the polypidom itself, so that its growth was 

 in some measure independent of the living tenant ; and various 

 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 with- 

 holding 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.f It seems probable, in fact, that neither theory will 

 explain the growth of all polypidoms; and as the peculiari- 

 ties which distinguish these are considerable, and would ren- 

 der a general description involved and obscure, I have given 

 the explanation of their mode of increase in the preface to 

 each separate order. Enough has in the meantime been said 

 to show how unimportant the polypidom must be as a pri- 

 mary character in a natural classification of zoophytes, and 

 yet, until very recently, no other basis was looked for or 

 deemed available, and hence the artificialness of the proposed 

 " Systems" which, as a matter of history, we now venture to 

 review. 



The main object of Ellis being to prove the animality of 

 zoophytes, he deemed a new classification of them unneces- 



* Encyclop. Method, art. Zoophyte. 



+ Milne Edwards and Mr. Couch have, perhaps, demonstrated that the polypidom 

 is an integral part of the animal, and subject to change from intus-susception. Besides 

 the references already given, see Ann. Nat. Hist. iii. p. 214. 



