ECHINODERMATA. 203 



especially the largest ones : their pedicel is long and slender ; their 

 capital resembles the bud of a flower, defended by three sepals, the 

 apex of each of which is produced inwards in the form of two pairs 

 of long and slender teeth. The quadridentate sepaloid plates can be 

 divaricated and approximated, and constitute a very effective pre- 

 hensile instrument : they are highly irritable ; a needle introduced 

 into their grasp is instantly seized. The ciliated gemmule of any 

 parasitic coralline, which might settle about the base of a spine, and 

 there commence its growth, would be liable to be seized and uprooted 

 by the prehensile gemmiform pedicellariae, which are of microscopic 

 minuteness. 



The tridactyle pedicellariae {Jig. 97, a) are of 

 larger size, are visible to the naked eye, and fit to 

 grapple with and dislodge young sedentary pa- 

 rasites of larger species, as Cirripeds and Con- 

 chifers. They are found more particularly around 

 the large tubercles of the interambulacral plates 

 which support the largest spines. Their capital 

 is longer, narrower, and more pointed than in 

 the gemmiform kind ; and the three pieces are 

 PediceiiariJE dcntated and close upon each other, like the blades 



of pincers. 

 The "pedicellariae ophicephalas" are aggregated principally upon 

 the buccal membrane. 



The pedicellarige of the star-fishes are diffused generally over the 

 surface, and form dense groups round the spines : they consist of a 

 slender contractile stem ; but the head resembles a forceps with two 

 blades (^fig. 97, b) : they are continually in motion, opening and 

 shutting their blades. They would wage as effective and serviceable 

 a war in defence of the integument of the Asterias against the 

 attacks of the host of parasites which the sea engenders as their 

 tridactyle analogues in the Echini may do. In some species of 

 Goniaster the pedicellarije resemble the vane of an arrow, and are so 

 numerous as to give a villous appearance to the integuments. 



The muscular system of the Echinus, into the details of which the 

 limits of the present lecture forbid me to enter, includes the muscles 

 of the spines, those of the jaws or lantern, of the buccal membrane, 

 of the anus, of the ambulacral tubes, of the internal branchiae, and of 

 the pedicellariae. The muscles of the lantern and spines have their 

 ultimate filaments collected into primitive fibres or fascicles, which 

 are marked by transverse striae at regular distances as in the muscles 

 of insects.* 



* CLXVIL p. 101. 



