ECHINODERMATA. 147 



of but one calcareous piece, are attached to the inferior margins of 

 each ray, sometimes in several rows ; and, being still moveable, they 

 may be useful in seizing prey, or even as assisting in progression. 

 Upon the dorsal aspect of the body are other calcareous projec- 

 tions, exhibiting a great variety of forms, so as to render the en- 

 tire surface of the animal uneven and tuberculated. 



But the most remarkable appendages to the integument of the 

 Asterias are minute bodies, which have been named by authors 

 Pedicellarice, and have been looked upon by many naturalists as 

 distinct animals, allied to polyps in structure, and living parasiti- 

 cally upon star-fishes and other ECHINODERMATA. Each of these 

 curious processes consists of a short stem fixed by one extremity to 

 the skin of the Asterias, and terminating at the opposite end in 

 two or three points resembling in some respects the prongs of a 

 fork : the stem itself does not seem to be perforated by any canal ; 

 but, nevertheless, the terminating points are found to be highly 

 irritable, and quickly seize hold of any minute body placed between 

 them. Some writers regard these bodies as organs of prehension, 

 used under certain circumstances for fixing the animals which 

 possess them ; but, from their small size and general appearance, 

 they seem but ill adapted to such an office. 



(189.) The skeleton or calcareous framework imbedded in the 

 skin of the Asteridse is by no means the least remarkable part of 

 their structure : this consists of several hundred pieces variously 

 disposed, and for the most part fitted together with great accuracy; 

 being either firmly soldered to each other, as we have seen them 

 to be in the formation of the calcareous box that constitutes the 

 central portion of Ophiurus, or united by ligaments, so as to allow 

 of a considerable degree of motion to take place between them, as in 

 the rays of Ophiurus, Gorgonocephalus, and other asteroid forms. 



In the generality of star-fishes, the arrangement, and indeed the 

 entire character of the calcareous plates, differs materially in differ- 

 ent parts of the body; and, even in different species, considerable 

 modifications are observable. In the coriaceous integument form- 

 ing the dorsal parietes of the animal, the pieces in many cases 

 seem rather to be represented by calcareous granules disseminated 

 through the interior of the skin, or in other cases they are ar- 

 ranged in lines anastomosing with each other in all directions, so as 

 to represent, when the skin is dried, a rude network of solid par- 

 ticles, upon the exterior of which the various cutaneous appendages 

 already noticed are sustained. 



