398 THE VOYAGE OF H.M.S. CHALLENGER. 



Echinoderm, which seems to be inseparable from Lov^n's use of the term. Should Prof. 

 Loven ever write anything more upon the apical system of Echinoderms, he cannot avoid 

 referring to the radial plates between the dorsocentral and the so called genitals (costals 

 or basals) of an Asterid. He cannot speak of them by the name which was given them 

 by Sladeu who discovered them, viz., " under-basals," for this term would be meaning- 

 less and confusing unless the plates outside them (the costals of Loven) were also called 

 basals ; and he would therefore have to invent a new name for them, a proceeding to 

 which he objects, or else adopt the terminology of Sladen and myself. I am sanguine 

 enough to hope, not only that this will be the case, but also that the presence in Asterids 

 and Ophiurids of plates homologous with the under-basals of Crinoids will lead him to 

 abandon his theory of the homology of these under-basals with the dorsocentral of an 

 Urchin or Starfish. I little expected six years ago to get so complete a confirmation of 

 the views I then expressed as the presence of a " dicyclic base " in several Asterids and 

 Ophiurids as well as in Cyathocrinus and Marsupites. The similarity in structure of 

 the apical system in all the groups of brachiate Echinoderms thus becomes exceedingly 

 striking ; and it affords a further proof (if such were needed) of the homology between 

 the apical systems of the Echinozoa and the Pelmatozoa respectively. 



Two authors, however, have been led to an entirely different conclusion respecting 

 the interradial abactinal plates of the Starfish larva from that of Loven, Agassiz, Sladen, 

 and myself. Ludwig regards them as homologous with the orals of a Crinoid, because 

 one of the latter is pierced by the primitive water-tube ; ^ while the madreporite of an 

 adult Starfish is in relation with one of the so called genital plates (costals or basals). 

 The morphological diSiculties inseparable from this inversion of the relations between a 

 Starfish and a Crinoid, as ordinarily conceived, have been discussed by Sladen" and 

 myself.' With the exception of Studer,* whose errors have been discussed elsewhere,® no 

 other writer has alluded to the subject ; though it has recently made its appearance in a 

 somewhat modified form. Perrier stated two years ago " that the primary interradial plates 

 around the dorsocentral of the young Brisinga develop into the so called odontophores 

 of the adult. The former are the plates which are usually known as the genitals (costals 

 of Loven ; basals of Sladeu and myself) ; and if Perrier's statement be correct, the views 

 of Loven, Agassiz, Sladen, and myself respecting the homology of the apical plates 

 through the whole group of Echinoderms are no longer tenable. No proofs of it have yet 

 been offered, however, though in a later note by Perrier " the following passage appears, 

 "Les jeunes Asteries, les jeunes Brisinga presentent aussi, comme Loven et nous-meme 



1 Zeitschr.f. wiss. Zool, Bd. xxxiv. p. 318, 1880. 



2 Quart. Journ. Micr. Sci., 1884, vol. xxiv., N. S., pp. 35-40. 



3 Ibid., 1880, vol. XX., N. S., pp. 322-329. 



* Uebersicht iiber die Ophiurideii welche -wiihrend der Eeise S.M.S. " Gazelle " iim die Erde, 1874-76, gesammelt 

 \nirden, Ablmndl. d. k. Akad. d. Wiss. Berlin, aus dem Jahre 1882, Phys. Kl. Abh., i. p. 10. 

 ^ Quart. Journ. Micr. Sci., 1884, vol. xxiv., N. S., pp. 15-18. 

 « Note sur les Brisinga, Comptes rendus, t. scv., 1882, p. 63. ^ Ibid., p. 1381. 



