ECHINOIDEA. 



223 



for the inner vation of the muscles and sensory epithelium. 

 Pedicellariae are found on all parts of the surface amongst the 

 spines. They are smaller and less numerous in the Irregularia 

 (Spatangoids and Clypeastroids) than in the Regularia. They 

 present considerable variation in 

 structure and are of great im- 

 portance in classification (Morten- 

 sen). 



There are four kinds of pedicel- 

 lariae : the globiferous (genimi- 

 form), the tridentate (tridactyle), 

 the ophicephalous, and the triphyl- 

 lous (trifoliate). 



(l)The globiferous pedicellariae (Figs. 

 165, 167, 1) have long stalks and are pro- 

 vided with a gland, which shows indica- 

 tions of being double, on the outer side 

 of each blade (on the inside in the Cida- 

 ridae) and in some cases (Sphaer echinus 

 granularis) with three glands half-way 

 up the stalk. The blade ends in a tooth 

 which is grooved on its outer side. 

 The gland of the blade opens on this 

 groove near the tip of the tooth and 

 secretes a viscid fluid which is supposed 

 to be poisonous. There is a patch of sen- 

 sory epithelium on the inner side of each 

 blade near its base and sometimes a 

 second nearer the apex. The axial cal- 

 careous rod extends the whole length of 

 the stalk and the blades are attached to 

 the end of it by a ligament. 



The so-called globifers are globiferous 

 pedicellariae, the distal parts of which 

 beyond the stalk-glands are absent or 

 reduced. They have the form of short 

 stalks ending in a trilobed swelling and 

 have been found in Sphaerechinus granu- 

 laris, Centrostephanus longispinus, etc. 

 Traces of blades are sometimes dis- 

 cernible on them. 



(2) The tridentate pedicellariae (Figs. 

 166 C, 167, 4) are the largest and most 



movable of these organs. Their mobility is due to the fact that the 

 distal end of the stalk is occupied by a rod of elastic tissue embedded in a 

 sheath of smooth muscular fibres, the axial calcareous rod not reaching 

 the whole way. The blades are long, broad at the base and narrow 

 distally, and they are provided with teeth along their edges. They are 

 usually without glands, and the adductor muscles are cross-striped. 



FIG. 165. Diagram showing the struc- 

 ture of a globiferous pedicellaria 

 (from Lang). 1, 3 sense organs ; 

 2 aperture of the gland of the blade ; 

 i adductor muscle ; 5 skeleton of 

 the blade ; 6 epithelium of the blade ; 

 7 gland of the blade, 8 its epithe- 

 lium ; 9 muscle-layer of the gland ; 

 10, 11 divaricator muscles ; 12 nerve ; 

 13 calcareous rod of the stalk ; 15, 

 16 gland of the stalk, 14 its aper- 

 ture. 



