ANTEDON 



901 



siderable activity, but it exerts this power chiefly to gain a suitable 

 place for attaching itself by means of the jointed prehensile cirrhi 

 put forth from the aboral (under) side of the central disc (fig. 685) ; 

 so that, notwithstanding its locomotive power, it is nearly as station- 

 ary in its free adult condition as it is in its earlier jpentacrinoid 

 stage. The pentacrinoid larva l first discovered by Mr. J. V. 

 Thompson, of Cork, in 1823, but originally supposed by him to be a 

 permanently attached Crinoid forms a most beautiful object for the 

 lower powers of the microscope, when well preserved in fluid, and 

 viewed by a strong incident light (fig. 686,3) ; and a series of specimens 

 in different stages of development shows most curious modifications 

 in the form and arrangement of the various component pieces 

 of its calcareous skeleton. Jn its earlier stage (fig. 686, l) the 

 body is inclosed in a 

 calyx composed of 

 two circles of plates, 

 namely, five basals, 

 forming a sort of 

 pyramid whose apex 

 points downwards, and 

 is attached to the 

 highest joint of the 

 stem ; and five orals 

 superposed on these, 

 forming when closed 

 a like pyramid whose 

 apex points upwards, 

 but usually separating 

 to give passage to the 

 tentacles, of which a 

 circlet surrounds the 

 mouth. In this con- 

 dition there is no 

 rudiment of arms. In 

 the more advanced 

 stage shown at 2, 



the arms have begun to make their appearance, and the skeleton 

 when carefully examined is found to consist of the following pieces, 

 as shown in fig. 686, l, b, b, the circlet of basals supported on the 

 top of the stem ; r 1 , the circle of first radials, now interposed between 

 the basals and the orals, and alternating with both ; between two 

 of these is interposed the single anal plate a ; whilst they support 

 the second and the third radials (r 2 , r 5 ), from the latter of which 

 the bifurcating arms spring ; finally, between the second radials we 

 see the five orals lifted from the basals on which they originally 

 rested by the interposition of the first radials. In the more advanced 

 stage shown in fig. 686, 3, we find the highest joint of the stem 



1 The pentacrinoid larvae of Antedon have been found abundantly (attached to 

 seaweeds and zoophytes) at Millport, on the Clyde, and in Lamlash Bay, Arran; in 

 Kirkwall Bay, Orkney ; in Lough Strangford, near Belfast, and in the Bay of Cork ; 

 and at Ilfracombe and in Salccmbe Bay, Devon. 



FIG. 685. Antedon (Comatula), or feather-star, 

 seen from its aboral side. 



