ECHINODERMA. 



121 



and more pointed than in the gemmiform kind ; and the three pieces 

 are dentated and close upon each other, like the blades of pincers. 



The " pedicellariae ophicephalae " are aggregated principally upon 

 the buccal membrane. •• 



The pedicellariae 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 : 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 pedicellariae resemble 

 the vane of an arrow, and are so numerous as to give a villous ap- 

 pearance 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. * 



The digestive apparatus of the Echinus {fig. 66.) consists of a 



mouth armed with teeth, surrounded 

 by a muscular labial membrane, and 

 five pairs of pinnate tubular ten- 

 tacula, of an oesophagus and sto- 

 mach, and of an intestine suspended 

 by a mesentery to the interior of 

 the shell, and which, after perform- 

 ing a few circumgyrations, termi- 

 nates by a distinct outlet opposite 

 to the mouth. The outer margin 

 of the lip is fringed by a circle of 

 the ophicephalous pedicellariae, vi- 

 sible to the naked eye. 



The teeth (a) are five in number ; 



they are calcareous, three sided 



Echinus. prisms, dense at the working apex, 



softer at the base, with the inner 



edge sharp and fit for cutting; they are each implanted in a larger 



Valentin, 1. c. p. 101. 



