Morphology o/*Antedon rosacea. 27 



of the centro-dorsal piece and through the five bundles of 

 muscular and other fibres, four flexor and one extensor, which 

 effect the articulation between the first and second radials. 

 An artificial rent, caused by the tearing away of the densest 

 part of the bundle of extensor fibres, is marked "y^, cavites 

 laterales de I'organe cloisound," namely the chambers marked 

 yin fig. 267, which are enclosed by the thick nervous enve- 

 lope of the central capsule, and are in the very middle of the 

 centro-dorsal plate. In fact the chambers of the " organe 

 cloisonne " lie inside what the authors describe as the "anneau 

 nerveux central ; " while the space marked f^ in fig. 268 is 

 on the outer side of this structure, and is separated from it 

 by almost the entire thickness of the first radial. The 

 explanation of fig. 268 contains other serious errors. The 

 two first radials are not specially distinguished, but are simply 

 marked " a, pieces constituant le sommet du calice ; " and 

 the authors continue, " c, muscles qui les reunissent." These 

 " muscles," however, unite the first radials not with one 

 another, but with the second radials, as explained above j 

 while the tissue uniting the two first radials laterally is 

 marked "^-, colonne de I'organe dorsal, effleurde." The extent 

 of the error here involved will be evident from inspection of 

 the (nearly) horizontal section represented in fig. 264 on 

 p. 522. Its centre is occupied by the dorsal organ, marked 

 g ; while the structure which is marked g^ in fig. 268 is the 

 outermost edge of what is here marked h and described as 

 an articular face separating the "pieces calcaires du sommet," 

 in other words the first radials. The authors do not seem to 

 have recognized the fact that a vertical section which passes 

 through the articulation between the first and second radials 

 could not possibly also pass through any part of the dorsal 

 organ at its base, for it is not merely within the nerve-penta- 

 gon inside the first radials, but in the very centre of the calyx 

 itself, as shown in their figs. 264 and 267. 



Another gross blunder of the same kind appears in the 

 explanation of fig. 276 on p. 550, where the fibres uniting 

 the centro-dorsal to the first radials are described as "6, 

 muscles entre le premier et le second radial." These fibres, 

 though represented in fig. 267, are not referred to in its 

 explanation, and the unwary student would thus be led to 

 inter from fig. 276 that some of the cirrus-nerves pass out 

 from the central capsule directly into the first radials, and 

 that the arm-nerves pass at once into the second radials ! If 

 the authors had distinguished the centro-dorsal from the first 

 radials in this figure it would have been some help to the 



