252 The British Star-Fishes. 



what we know of the nature of this sense generally in the 

 lowest forms of animal life we should be disposed to consider 

 that the organs in question must serve some other as yet 

 unknown purpose. Other animals not far from the Star-fishes 

 in general organization, though possessing, so far as we know, 

 no special visual apparatus, are yet extremely sensitive to light, 

 and this sensitiveness seems to consist of a nervous irritability 

 shared by every part of the body, higher in degree, but possibly 

 of a nature somewhat analogous to that of similar manifestations 

 observable in plants. 



The upper or dorsal surface of the Star-fish presents ap- 

 pearances differing very considerably in different genera. It 

 may be perfectly smooth; it may be rough with tubercles or 

 bristling with spines, and it is the various forms of these 

 appendages to which we wish at present specially to devote ouy 

 attention. The genera Ophiura and Ophiocoma (Sand-stars 

 and Brittle-stars) may be easily recognized by the great length 

 and tenuity of their rays, and their excessive fragility. The 

 whole surface, both of disk and rays, is covered by scales 

 which are so closely appressed as to give an almost perfectly 

 smooth surface. These scales are arranged in definite and 

 often in very beautiful patterns, and in some species the 

 primary scales are edged or encircled by series of circular 

 bosses or tubercles, giving an exquisitely " rosulated" aspect 

 to the disk and rays. An example of this is given in Fig. 1 of 

 the tinted plate, which is a representation of the disk and 

 bases of the rays of Ophiocoma bellis. Though the surface of 

 the disk is in mature individuals of these genera mostly smooth, 

 many of them are when young closely beset with spines, and 

 in some cases these are persistent even in mature age. The 

 disk of Ophiocoma Goodsiri is not unfrequently thus clothed. Its 

 spines are represented at a in the tinted plate ; b of the same 

 plate illustrates the spines, which cover the disk of young 

 Ophiocoma rosala. The rays are in these genera constantly 

 provided with numerous spines which serve as locomotive 

 organs, differing, however, very widely in length and strength. 

 Ophiocoma filiformis has its spines frequently tipped with curi- 

 ous anchor-shaped processes (fig. e), which are supposed to 

 facilitate the motion of the creature over the muddy bottoms 

 which it frequents. In Ophiura they are very short, and not 

 apparent without careful inspection ; while in Ophiocoma they 

 are so long as to give quite a bristly, spinous appearance to 

 the animal, being sometimes, in fact, very much longer than 

 the breadth of the rays. The gradual development of the 

 spines of 0. rosula has been carefully studied by Mr. Hodge.* 

 In their early stages they are armed with hooks at the extre- 

 * Transactions of Tyneside Naturalists Field Club, vol. v., p. 41. 



