SPONGES AND ZOOPHYTES. 137 



a specimen of this is first torn from the rock to which it has attached 

 itself, it contracts into an unshapely mass, whose surface presents nothing 

 but a series of slight depressions arranged with a certain regularity. But 

 after being immersed for a little time in a jar of sea-water, the mass 

 swells-out again, and from every one of these depressions an eight-armed 

 polype is protruded, "which resembles a flower of exquisite beauty and 

 perfect symmetry. In specimens recently taken, each of the petal-like 

 tentacula is seen with a hand-glass to be furnished with a row of 'deli- 

 cately-slender pinncB or filaments, fringing each margin, and arching 

 onwards; and with a higher power, these pinnae are seen to be roughened 

 throughout their whole length, with numerous prickly rings. After a 

 day's captivity, however, the petals shrink up into short, thick, unshapely 

 masses, rudely notched at their edges" (Gosse). When a mass of this 

 sort is cut-into it is found to be channelled-out somewhat like a Sponge, 

 by ramifying canals; the vents of which open into the stomachal cavities 

 of the polypes, which are thus brought into free communication with 

 each other, a character that especially distinguishes this Order. A 

 movement of fluid is kept-up within these canals (as may be distinctly 

 seen through their transparent bodies) by means of cilia lining the inter- 

 nal surfaces of the polypes; but no cilia can be discerned on their external 

 surfaces. The tissue of this spongy polypidom is strengthened through- 

 out, like that of Sponges ( 510), with mineral spicules (always, however, 

 calcareous), which are remarkable for the elegance of their forms; these 

 are disposed with great regularity around the bases of the polypes, and 

 even extend part of their length upwards on their bodies. In the Gor- 

 tjonia, or sea-fan, whilst the central part of the polypidom is consolidated 

 into a horny axis, the soft flesh which clothes this axis is so full of 

 tuberculated spicules, especially in its outer layer, that, when this dries-up 

 they form a thick yellowish or reddish incrustation upon the horney 

 stem; this crust is, however, so friable, that it may be easily rubbed 

 down between the fingers, and when examined with the Microscope, it is 

 found to consists of spicules of different shapes and sizes, more or less 

 resembling those shown in Figs. 362, 303, sometimes colorless, but some- 

 times of a beautiful crimson, yellow, or purple. These spicules are best 

 seen by Black-ground illumination, especially when viewed by the Bino- 

 cular Microscope. They are, of course, to be separated from the animal 

 substance in the same manner as the calcareous spicules of Sponges 

 ( 512); and they should be mounted, like them, in Canada balsam. The 

 spicules always possess an organic basis; as is proved by the fact, that 

 when their lime is dissolved by dilute acid, a gelatinous-looking residuum 

 is left, which preserves the form of the spicule. 



530. The Ctenophora, or ' comb-bearers/ are so named from the 

 comb-like arrangement of the rows of tiny * paddles/ by the movement 

 of which the bodies of these animals are propelled. A very beautiful 

 and not uncommon representative of this order is furnished by the Cy- 

 dippe pileus (Fig. 364), very commonly known as the Beroe, which 

 designation, however, properly appertains to another animal (Fig. 365) 

 of the same grade of organization. The body of Cydippe Is a nearly- 

 globular mass of soft jelly, usually about 3-8ths of an inch in diameter; 

 and it may be observed, even with the naked eye, to be marked by eight 

 bright bands, which proceed from pole to pole like meridian lines. 

 These bands are seen with the Microscope to be formed of rows of flat- 

 tened filaments, far larger than ordinary cilia, but lashing the water in 

 the same manner; they sometimes act quite independently of one 



