220 Charles Lincoln Edwards 



able to determine because of the lack of stages between the thirty- 

 third day, with no trace of the sixth tentacle, and the fortieth day 

 with the sixth developed and the seventh budded. A second forty-day 

 specimen, showing precocious development, has in addition, the buds 

 of the eighth tentacle dorsad from the right dorsal radial canal (D 8) 

 and the ninth and tenth (R and L, 9, 10), ventrad from the right 

 and left ventral radial canals. Thus for the first time, at the fortieth 

 day, is a tentacle (D8) given off from the right dorsal radial canal, 

 although so early as the twenty-fourth day this canal has evaginated 

 a j)apilla. In some specimens the ninth tentacle first appears on 

 the left, in others, on the right, but in most cases these two appear 

 at the same time. In the forty-second day the eighth tentacle is 

 found externally (PL III, Figs. 11-14, RDdl). A forty-nine day 

 specimen presents the bud of the eleventh tentacle from the primary 

 tentacular canal to the right of the mid-ventral radial canal (Dia- 

 gram 1, V 11) one at seventy-one days shows a small tentacle, the 

 twelfth, from the canal of the primary tentacle to the left of the 

 mid-ventral radial canal (V 12), and one at seventy-five days, the 

 thirteenth (D 13), from the primary tentacular canal dorsad from 

 the left dorsal radial canal (PL III, Figs. 13-14, LDd2). Thus, in 

 the development of the adult symmetry, as represented in Diagram 1, 

 by the end of my ontogenetic series, the following tentacles have ap- 

 peared, albeit not all in any one holotliurid ; the four from the mid- 

 ventral radial canal, the two dorsal and one of the ventral from each 

 of the lateral ventral radial canals, the two dorsal from the left 

 dorsal radial canal and only one from the right dorsal radial canal. 

 In general, beginning with the fifth, the tentacles develop in alterna- 

 tion from left to right. 



By the eighth day the suckers of one or more of the tentacles are 

 divided. Later these halves divide and the dichotomous branching 

 of the adult tentacle is established. (Pis. II-III, Figs. 7-14). 



By the sixty-seventh day the tentacle ampullae have become devel- 

 oped and can be followed in cross-sections from their place of origin 

 from the bases of the tentacular canals at the anterior end of the 

 calcareous ring to about one-half the distance back to the circular 

 canal. The origin of the tentacle ampullas does not seem to have 

 been previously noted. 



