CALAMOCRIXUS DIOiMED.E. 93 



upon which he bases his classification of the Echinodenns * falls to the 

 tyrouutl. 



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

 still remain that the tentacular system is entirely a product of the left 

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

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

 Bipinnaria.f So that in either case the matter (1(jos not lie quite as simply 

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

 stafe to a Pentactula statje the axis of the Echinoderm is so twisted that 

 the right 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 the transition from the bilateral to the radial type was a 

 fixed fact. This is carrying assumptions very far into the nebulous origin 

 of thinifs. 



I 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 1864 to its value in determining tlie 

 axis of Echini and Starfishes. 



Loven, in 1871, :j: sa3-s : "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 tlie 

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

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

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

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

 in the relations of the radioles and pedicellarire." 



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 Ttudes sur les Echinoidees, where he says, " et Ton est 



* The types of the Criiioids, Oi>lniirans, and Starfishes he bases upon the well known structural 

 features of the extension of the body cavity, of tlie 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 

 honiologies 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 deyelopment of the actinal 

 and abactinal systems of Echinoderms due to Goette ; it was already observed in 1804. 



t See Embryology of the Starfish, 1804. 



% See translation of Loven's article by Dallas in .\nn. and ^lag. of Xat. Ilist,, 1872, Vol. X. p. 429. 



