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 Gorgonise 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 neAv parts ; but so far from hav- 

 ing anything in common — any affinity with the proper polypidoms 

 of the Hydroida 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 hrmness 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. 



