218 



Charles Lincoln Edwards 



9,IO 



A ^^ [^ A5 



^11 12 



Diagram I. Order of development of thirteen of the twenty tentacles con- 

 stituting the adult symmetry. The vertically hatched central oesophagus is 

 surrounded by the circular canal of the water-vascular system, from which 

 the five radial canals arise. The five radialia, and the five interradialia, are 

 hatched diagonally. At the base of each radiale, the radial canal gives 

 off two tentacular canals to each side and then proceeds anteriorly, turning 

 through the notch into the body- wall. The first tentacular canal to be 

 developed runs along the inner surface of the radiale-interradiale joint 

 and the second, having been evaginated from the base of the first, goes along- 

 side of the radial canal. At the anterior margin of the calcareous ring, 

 the tentacular canals give off the ampullse and then terminate in the peltate 

 tentacles. The ampulhie hang down behind the calcareous pieces, and, as they 

 come into view, are seen outlined against the cross-hatching which represents 

 the ccBlom. 



D. Dorsal. V. Ventral. R. Right. L. Left, dl, d2, vl, v2. Tentacles 

 dorsad and ventrad respectively, in the order of development from' a given 

 radial canal, rl, r2, 11, 12. Tentacles to the right, and to the left, respectively, 

 in the order of development from the mid-ventral radial canal. A. One of 

 the first four primary tentacles. A5. The fifth primary tentacle. 6, 7, 8, 9, 

 10, 11, 12, 13. Secondary tentacles in serial order of development. 



