Natural History of British Zoophytes. 443 
longation 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 Raster opposed Ellis, and believ- 
ed in a vegetative principle, inherent in the polypidom itself, so 
that its growth was in some measure independent of the living ten- 
ant ; and various arguments have been brought forward by Bory 
de St Vincent, which appear to him to demonstrate the truth of 
this doctrine. 
Let us forget their reasonings, and take a concise review of the ' 
facts. The polypes of Pennatula and Alcyonium occupy cells, which 
are, as it were, immersed in a pulpous mass, containing a consider- 
able quantity of calcareous spicula, and which appears to be living 
and organized ; for if the naked stem of the Pennatula, or the sur- 
face of the Lobularia is irritated, a slow gradual contraction of the 
whole polypidom apparently proves that the irritation has been felt 
throughout ; and if left undisturbed for a time, the polypidom will 
be again distended, until its bulk exceeds by two or three times its 
dimensions in the collapsed state ; the increase in size being pro- 
duced by the introduction of water into the interior, and which has 
percolated, as has been shown, through the stomach and vasculiform 
appendages of the polypes. The crust or bark of the Gorgoniae is 
identical in structure with the Alcyonium, and, like it, also a living 
part, capable of converting nutriment to its own nature, of repairing 
injuries and losses, and of forming new parts ; but so far from hav- 
ing anything in common any affinity with the proper polypidoms 
of the Kydroida and Ascidioda, this crust is in fact identical with 
the medullary pulp of the latter, and the very source of what Ellis 
and Lamarck would consider the inorganic polypidom. * For it is 
to be observed, that in the Asteroid (which includes Pennatula, 
Alcyonium and Gorgonia) the polypes and their medium of union 
are external or cortical ; there is strictly speaking no polypidom, 
but the part which a strict analogy teaches us to call so, is the 
central solid axis which gives form and firmness to the structure. 
Now, when we trace the formation of this axis through the various 
genera, from its first appearance in the form of scattered crystalline 
spicula, until it graduates into a solid continuous rod, we can 
scarcely doubt its inorganic and extravascular character ; it is the 
* Bosc takes a different, and a strangely erroneous view : He conjectures 
that the polypes of these polypidoms may have excretory pores of two kinds, 
one kind situated at the posterior part of the animal, to give exit to the juice 
-which is converted into the horny axis ; the other kind placed in the collar to 
excrete the cretaceous or spongoid bark Vers, ii. 226. 
