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



insequalis, and Antedon breviradia (PL I. fig. 8c ; PI. II. figs. 3c, 5c ; PI. III. figs. 4c, 

 56), and also in those of Actinometra maculata, Actinometra lineata, and Actinometra 

 stelligera (PI. V. figs, lc, 2c, 2c, 5d, be). Owing to its homologies with the basals of 

 other Crinoids, and through these forms with the corresponding plates in other Echino- 

 derms (e.g., the genitals of Echini), it is a very important structure, apart altogether 

 from its intimate relation to the great nerve centre lodged within the centro-dorsal plate 

 and to the axial cords proceeding from it. 



One would have thought therefore that some account would have been given of it in 

 Vogt and Yung's work upon practical comparative anatomy in which Antedon rosacea, 

 the form studied by Dr. Carpenter, is taken as a type of all Crinoids. It is dismissed, 

 however, in less than half a dozen lines, and not a word is said of its morphological 

 relations. In fact the word "basals" does not once occur in the chapter on Crinoidea 

 in the treatise by Messrs. Vogt and Yung, who pay no attention to the comparative 

 anatomy of anything but the soft parts as revealed by thin microscopic sections. 

 Unfortunately, however, this too exclusive reliance upon one method of investigation 

 has led them into a serious but at the same time a somewhat ludicrous error. In the 

 figure given by Messrs. Vogt and Yung 1 " pour montrer la disposition du systeme 

 nerveux central et des organes dorsal et cloisonne " the chambered organ (as originally 

 described) is covered by a structure marked o. No explanation of this letter is given, 

 but I learn from Professor Carl Vogt that the missing explanation should be — o, tissu 

 conjonctif areolaire entourant 1' organ e dorsal et les cavities c de l'organe cloisonne'. 



Now this structure which is marked o in Vogt and Yung's fig. 276 is in reality 

 nothing more or less than a part of the rosette of modified basals, which in the natural 

 position of the animal roofs in the internal cavity of the centro-dorsal that contains the 

 chambered organ, as is well shown in PL V. figs. 2c, 2e, and 5c. The relations of this 

 structure to the soft parts beneath it are entirely ignored by Messrs. Vogt and Yung, 

 though they were described at length by myself in 1879 2 and again in 1881. In the 

 latter year I published two sectional views 3 showing the position of the rosette with 

 respect to the chambered organ, and another similar figure and description were given 

 later on by Marshall. 4 But these have been altogether ignored by Messrs. Vogt and Yung, 

 who have also neglected to work out the point for themselves ; and the consequence is that 

 a structure which, though small and insignificant in Comatulse, is nevertheless homologous 

 with the five genital plates of Echini, is figured in a textbook of comparative anatomy as 

 " areolar connective tissue." In the same figure, too, a portion of the centro-dorsal piece, 

 which is in immediate contact with the central capsule, is lettered " e, mesentere." 



There are many other points in the relations of the Crinoid skeleton which are 



1 Op. tit., p. 550, fig. 276. 2 Trans. Linn. Soc. Lond. (ZooL), 1879, ser. 2, p. 78. 



3 The Minute Anatomy of the Brachiate Eehinoderms, Quart. Journ. Micr. Sci., 1881, vol. xxi., N.S.,p. 186, pi. xii. 

 figs. 14, 15. 



1 Lot. cit., pp. 508, 511, pi. xxv. fig. 1. See also Ludwig, lot. tit., Taf. xix. fig. 74. 



