THE CR1NOIDEA 



101 



containing the genital cord or rachis (g.c) and a " coeliac canal " 

 (c.c). On either side of the water-vessel, beneath the tentacles, is a 

 senso-motor nerve (/i2), giving off branches to the muscles of the 



a.c 



Pio. VII. 

 Diagram of solid section of a Crinoid arm. For explanation of letters see adjoining text. 



water-canals and to sensory papillae (s) on the tentacles. Below 

 all these, in a special groove on the very floor of the main brachial 

 groove, lies another nerve, the " axial cord " (a.c), proceeding from 

 the aboral or dorsal motor nerve- system ; the groove in which this 

 lies is often (as in Fig. VII.) separ- 

 ated from the brachial groove 

 during individual development 

 by an outgrowth of stereom, and 

 is then known as the " dorsal " or 

 " axial canal " (Fig. VIII.). The 



ivial r>nrr\ <?pnrls5 nff hranrhps (n^\ 

 nes (113) 



to all the muscles of the arms, 

 and to supposed sensory endings in the ectoderm (ed}, and is con- 

 nected with the subtentacular nerves. All these soft structures 

 in the ventral groove are protected by covering-plates (c.p), also 



X. 



FIG. VIII. 



Staffs in the separation of an axial canal, 



exemplified by brachials of Gissocrinus gnnio- 



: 1 is youngest ; 4, oldest. X ' diain. 



