166 ZOOPHYTA ASTEROIDA. 



trary, when at rest and undisturbed, the polypes protrude their 

 tentacula and a portion of the body, and, imbibing the circum- 

 fluent water, this percolates into the interior through numerous 

 anastomosing canals, and distends the polypidom so much that 

 it will more than double or treble its former size. In this re- 

 spect the Zoophyta asteroida show an affinity to the Helianthoida, 

 and differ from the hydraform and more especially from the as- 

 cidian orders. 



The axis of the Alcyonidse is imperfect, but exists neverthe- 

 less in the form of calcareous or siliceous spicula diffused through 

 the gelatinous interior, or more or less densely clustered at the 

 centre; and the appearance of these spicula is such that we 

 are almost tempted to believe they may possibly be the products 

 of crystallization rather than of any regular secretion.* It might 

 not be difficult, but it is beyond my province, to trace the gra- 

 dual increase and consolidation of these spicula through many 

 intermediate species to the horny flexible axis of Gorgonia, 

 where it has become such an efficient support to the whole soft 

 envelope as to claim not improperly the name of its skeleton ; 

 thence to the stony axis of the coral ; and having there reached 

 its maximum of developement, I might, on the other hand, have 

 marked its progress towards degeneration until it became again 

 only a partial support, such as we find it in the naked middle 

 portion of the Pennatulidae, more especially in some of the fo- 

 reign and less typical species of that family. 



According to Lamarck, this axis, under all its modifications, is 

 inorganic, containing neither vessels nor any portion of the 

 body of the polypes, but formed of matter excreted by them, 

 and afterwards thickened, solidified and depurated by af- 

 finity.-f- Although this is rather, on Lamarck's part, the de- 



Successive births her tender cares combine, 

 And soft affections live along the line." 



DarwiiVs Temp, of Nature, canto ii. 

 * They may be compared with the Raphides found in the intercellular pas- 

 sages of certain monocotyledonous plants. See Lindley's Introd. to Botany, 



p. 29 Mr Children found in the ashes of a piece of the axis of Gorgonia 



Flabellum, a distinct trace of pure silica, sufficient to form a globule before the 



blow-pipe Ann. of Philosophy, New Series, Vol. ix. p. 43). 



t " L'obscrvation constate que I'axe central de ccs polypiers, quoiqu' offrant 

 quelquefois dcs couches concentriqurs, ne fut jamais organise, n'a contenu ni 

 vaisseaux quelconques, ni aucune portion du corps dcs polypes ; qu'il est le 

 rcsultat dc matieres excretees par ces polj'pes, matieres qui se sont epaissies, 



