FORMS OF THE POLYPIDOMS. 
55 
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 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 ceils, 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- 
nseus, 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 'primary 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 artificialness 
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 Synopsis of 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 Syn. Meth. Stirpium Brit. Edit. 3. Loud. 1724. 
