rOLYPlFERA. 



25 



Fig. 29. 



Hydra fusca, containing the larva of an insect par- 

 tiaUy digested. 



o, large superficial cells of the integument ; I, mus- 

 cular stratum, the cells of which are 

 very minute, granular, and coloured ; 

 c, villous tunic ; d, anus ; e, hollow 

 membranous prolongation or foot. 

 (After Corda.) 



water, however, and allowing it to remain for 

 a little time undisturbed, its real nature be- 

 comes apparent and a series of most interest- 

 ing phenomena present themselves. The mass, 

 which was at first opaque and of a dense tex- 

 ture, slowly swells and becomes more diapha- 

 nous, apparently by the absorption of the 

 surrounding water into its substance, until, 

 having attained its full dimensions, numerous 

 dimples appear, studding its entire surface, 

 each of which, as it gradually expands, reveals 

 itself to be a cell, the residence of a polype, 

 which, emerging from its abode, displays eight 

 pinnated arms, and the entire Alcyon, thus 

 studded with living flowers, presents a spec- 

 tacle of extraordinary beauty, but if disturbed 

 speedily withdraws from observation and again 

 shrinks into its former shapeless condition. 



M. Milne Edwards * has thrown considerable 

 light upon the organization of these beautiful 

 structures by his indefatigable researches, the 

 results of which we shall lay before the reader 

 at some length, as they are of great importance 

 in illustrating the economy of the polypiferous 

 zoophytes. 



The genus Alcyomde (fig. 30) has the poly- 

 pes grouped together in great numbers upon 

 the surface of a soft cylindrical polypary or 

 common body, which consists of two portions. 

 The lower portion (6), which is attached by 

 its base to fuci or other submarine substance, 

 is of a brown colour and firm texture, whilst 

 the upper part is white, membranous, and ex- 

 tremely delicate, divided into branches the 

 summits of which are crowned with elegant 

 polypes (d) of almost microscopic dimensions. 

 Each of these polypes has eight pinnated ten- 

 tacles, in the centre of which is the opening 

 of the mouth. 



Fis. 30. 



A group of Alcyonidcs (Alcyonidimn flrc/nns) fixed 

 to a marine plant, of the natural size. Ori two of the 

 great divisions of the polypary the animals are com- 

 pletely developed, whilst in the third (V) the whole 

 of the soft portion of the polypary is contracted and 

 withdrawn within the basilar portion, a, branch 

 to which the polypary is fixed ; b, foot or basilar 



portion of the polypary ; r, trunk or membranous 

 portion ; d, polype-bearing branches ; f, yellowish 

 spots occasioned by the presence of ovules in the in- 

 ferior portion of the trunk. (After Milne Edwards*) 



* Ann. des Sc. Nat. torn. iv. 1835. 



