C iXAMOCRINl S DIOMED l 



upon which he liases his classification of the Echinoderms ' falls to the 

 ground. 



Bui even granting Bury's observation to be correct, the fact would 

 still remain thai the tentacular .system is entire^ a produci of the lefl 

 water tube, and the early stages of the abactinal system are developed upon 

 the righl water tube before it has reached the anterior extremity of the 

 Bipinnaria.f So that in either case the matter does not lie quite as simply 

 as Semon imagines, when he tells us that in the passage from a Dipleurula 

 stage to a Pentactula stage the axis of the Echinoderm is so twisted that 

 the riglit side of the Dipleurula passes to the abactinal, and the left to 

 the actinal side. Semon takes this twisting to be well explained by the 



assumption that tie' transition from the bilateral to tie' radial type was a 

 fixed tact. This is earning assumptions very Car into the nebulous origin 

 of things. 



1 fully agree with Ludwig as to the importance of regarding the plane 

 in which the madreporic body is placed as of primary importance, and 

 have called attention as far back as 1S64 to its value in determining the 

 axis of Echini and Starfishes. 



Loven, in 18714 says: "Thus the asymmetry in the Echinoidean skel- 

 eton, with relation to its anterioposterior axis (an artificial axis existing 

 in Spatangoids and assumed for regular Echini) is expressed within each 

 ambulacrum, in its two subordinate rows of plates, most strikingly in the 

 arrangement, size, form, changes, and movements, during growth of the 

 peristomial plates and those immediately following them, in the number and 

 position of their pores, in the order of the appearance and disappearance 

 of the sphaeridia ; and it will probably not fail, upon closer investigation, 

 in the relations of the radioles and pedicellariae." 



That Loven considered his anterio-posterior axis a feature acquired sub- 

 sequently to the original axis for which I am claiming prominence as 

 the primordial axis of the pluteus, is clearly shown in his own words, on 

 page 39 of the Etudes sur les Echinoidees. where he says. " et Ton est 



* The types of the Crinoids. Ophiurans, and Starfishes he bases upon the well known structural 

 features of the extension of the body cavity, of the genital organs, and of the diverticula from the di- 

 gestive cavity into the tentacular region. He will find in the older writers (see L. Agassiz on the 

 homologies of Radiates) very much the same characterization of the different types of Echinoderms 

 which he attributes to Goette. Nor is the discovery of the difference in the development of the actinal 

 and abactinal systems of Echinoderms due to Goette ; it was already observed in 1S04. 



t See Embryology of the Starfish, 1864. 



t See translation of Loveu's article by Dallas in Ann. and Mag. of Xat. Hist., IS72, Vol. X. p. 429. 



