Development of Holothuria Floridana Poiirtales 221 



A. Discussion of Litekatuke. 



Kowalevsky, 1867, describes in Cucumaria kirchsbergii and Cucu- 

 maria planci and Selenka, 1876, also in Cucumaria planci, the forma- 

 tion, at first of three dorsal, and then later, of two ventral tentacles. 

 Ludwig, 1891a, states that in Cucumaria planci and, 1898, in 

 Phyllophorus urna and Clark, 1898, that in Synaptula hydriformis, 

 all of the five primary tentacles appear at the same time. Ludwig, 

 1891, also describes in Cucumaria planci an asymmetrical develop 

 ment of the tentacles but of a somewhat difterent pattern from that 

 which I find in Holothuria floridana. In agreement with my re- 

 sults, Ludwig shows that two of the five j)rimary tentacles are 

 given off from the mid-ventral radial canal, one to either side, 

 but, of the three others, two arise from the left dorsal radial 

 canal, dorsad and ventrad respectively, and one ventrad from the 

 right dorsal radial canal. Thus each of the right and left ventral 

 radial canals gives rise to a primary tentacle in Holothuria floridana 

 and does not in Cucumaria planci. Up to this time the determina- 

 tion of the exact origin of the tentacles from definite radial canals 

 has been made only in Cucumaria planci and Phyllophorus urna by 

 Ludwig and in Holothuria floridana by myself, with the above diverg- 

 ent findings. When other holothurians are studied in a similar 

 manner, it will be of interest to see whether these differences are 

 generic, or specific, and if yet other such peculiar asymmetrical dis- 

 tributions of the tentacles prevail. So it would appear that the gen- 

 eralization of Becher, 1907, 1908, that in addition to the mid- 

 ventral radial canal the left, and to a less degree the right dorsal 

 radial canals were the more important in the primitive ancestral 

 holothurian, is scarcely justifiable at present. The simple primitive 

 pedicel-like structure and function of the tentacles in the early 

 larvse of Holothuria floridana is like that described by Becher, 1907, 

 in the adult Ehabdomolgus ruber. 



Relative to the increase in number of the tentacles beyond the 

 primary five, we have but few observations. Danielssen and Koren, 

 1856, describe the appearance of distinct traces of five new tentacles 

 in Holothuria tremula on the forty-seventh day. In nine days these 

 buds grow to about the full size of the primary tentacles. In view 



