ECHINODERMATA 639 



serving as teeth. The food of some species consists of animals cap- 

 tured by the arms : others shovel mud into the mouth with the ad- 

 jacent tube feet and digest the food it contains. There is no anus. 

 The madreporite, aboral in the young, becomes oral in the adult 



Fig. 444. A, Ophiura. Oral surface of disc and part of the arms. B, Ophio- 

 glypha. Aboral surface. From Woods. 6. buccal plates; c/. upper ("dorsal") 

 plates of arms; g. genital slits; /. lateral plates of arms; r. radial plates; 

 V. under ("ventral") plates of arms. 



ver. 

 In.m. 



tiss. cqe. ^^^^^ 



:^ la.plL /V^ 



epin. ', Ta 

 ra.n. 



.'peh:\ %J^ 



Fig. 445. A section through an arm of an ophiuroid. Diagrammatic, magni- 

 fied. From Shipley and MacBride. coe. coelom; d.plt. upper plate; epin. 

 epineural canal ; la. pit. lateral plate ; In.ni. longitudinal muscle ; ped.ga. pedal 

 ganglion ; ra.n. radial nerve cord ; ra.peh. radial perihaemal canal ; ra.wv. 

 radial water vascular canal ; sp. spine; tf. tube foot; tiss. soft tissue supporting 

 plates; ver. "vertebra"; v. pit. under plate. 



because the disc, growing independently of the arms,- and faster 

 aborally, comes to overhang in the interradii. In coming over, the 

 madreporite brings with it the axial sinus, stone canal, axial organ 

 and madreporic vesicle, which are all orally placed. The gonads open, 

 not directly to the exterior, but into genital bursae, of which one opens 



