2 Dr. P. IT. Carpenter 07i the 



•wliicli homologies are universally recognized, though the 

 fact does not appear in the nomenclature. 



1. The use of the term ^^ Water -tube.'''' 



The term "water-tube" seems to have been first used by A, 

 Agassiz * for the two coelomic diverticula of the archenteron 

 in the Starfish-larva, this being " the name whicli denotes 

 most appropriately the function they assume of circulating 

 water through the body of the larva." He also applied the 

 same name f to the gills or " papulae " of Stimpson and 

 Sladen, which are not developed till much later ; but the first 

 meaning which he gave to the term has not found acceptance 

 in Europe, especially since the morphological importance of 

 these water-tubes has been more fully realized, and they have 

 been variously known as the coelomic pouches, vaso-peritoneal 

 sacs, &c. ; while " water-tube " or " tube hydrophore " has 

 been largely used by both English and French writers instead 

 of the misleading term " sand-canal " or " stone-canal," which 

 is so often totally inapplicable to the structure it is supposed 

 to designate. In America, however, Brooks J and Fewkes 

 have continued to speak of the water-tubes of the Echinoderm- 

 larva, and they use the same term when referring to the organs 

 which are described as circular and radial Water-vessels by 

 European writers. This course seems likely to lead to much 

 confusion, the more so as one at least, and sometimes both, of 

 the larval coelomic pouches do not in any way give rise to the 

 "water-tubes" of the ambulacral system. Fewkes is an 

 especial offender in this respect, for in his last publication but 

 one he uses the term water-tube with different meanings on 

 two successive lines § : — " Each of the five small cuh-de-saCy 

 r w, from the water tube on the ambulacral side of the young- 

 starfish forms a radial water tube of the starfish," Five 

 pages later he says that the stone-canal is an internal calcifi- 



diff(5reBts, cr6eut, dans I'esprit du lecteur, ime confusion p^nible qu'il est 

 parfois difficile d'^claircir par ime seule lecture et qui a contribuiS, pour 

 une large part, k faire prendre dans certains cas, comme divergentes, des 

 opinions qui ne difieraient pas sensiblenieut I'une de I'autre " (" Reclierches 

 sur les Holothuries des C6tes de France," Arch. Zool. Exp. et Gen. 

 vol, \ii. 1889, p. 030). 



* ' Embryology of the Starfish,' 1S64. Reprinted in *' North American 

 Starfishes," Mem. Mus. Comp. Zool. 1877, vol. v. p. 13. 



t Iljid. p. 62. 



I ' Handbook of Invertebrate Zoology,' Boston, 1882, pp. 72, 135. 



§ " On the Development of the Calcareous Plates of Asterias," Bull. 

 Mus. Comp. Zool. 1888, vol. xvii. p. 7. 



