58 ECHINODERMATA. 



certainty whether these were peculiar organs of the 

 Urchin, or parasitic animals that lived upon its 

 body : the former is now, however, ascertained to 

 be the true state of the case. These organs, which 

 are termed pedicellaria, are diverse in shape ; but in 

 general they may be described as consisting of a 

 thick head, cleft into three divisions, and set on 

 a long, slender, flexible stalk. Through a portion 

 only of the stalk passes an inflexible shelly sup- 

 port, like a bone; but there is left a considerable 

 part which is perfectly soft, flexible, and highly 

 contractile ; and by the motions of this part, the 

 massive head is thrown about in all directions with 

 great vivacity. In the common Urchin (Echinus 

 splicer CL], the largest sort of pedicellaria has a head 

 shaped something like a sugar-loaf, split from the 

 apex to the base into three lobes, which gape widely, 

 and close together with most ferocious snappings. 

 These openings and shuttings of the threefold jaws 

 are constantly going on, fitfully, and without any 

 regularity or agreement ; and most interesting it is 

 to watch them, and to endeavour to discover what 

 possible end is accomplished by the procedure. 



If we examine these bodies with high micro- 

 scopic powers, little light is afforded on the question 

 of their special functions, though it is thus that 

 they are determined to be organic appendages of 

 the Echinus. But new admiration is excited at 

 their elaborate structure and finish. The head 

 consists principally of calcareous substance, which, 

 as well as the supporting column of the stalk, is 

 penetrated with isolated cells throughout. The 

 bases of the three -lobed heads are articulated in the 

 most remarkable manner; and the lobes themselves, 

 which are sometimes attenuated to three slender 



