32 Dr. P. H. Carpenter on the 



of the descriptions and figures given by Dr. Carpenter, Lud- 

 wig, Marshall, or myself, they would know that a section in 

 the axis of a radial could not by any possibility show an 

 uninterrupted continuation of the nerve-cord direct from one 

 of the angles of the central capsule into the origin of an arm. 

 The arm-nerves start from the angles of the chambered organ, 

 which are interradial, and they occupy this position on the 

 dorsal surface of the calcareous rosette, where they bifurcate. 

 The left branch of one fork and the right branch of its 

 neighbour enter the same first radial, and a section through 

 the axis of the radial would not therefore pass through the 

 primary interradial cord arising from the central capsule. 

 Truly radial sections, such as those figured by Marshall* 

 and myself tj are not very difficult to obtain, and they show 

 the relations of these primary nerve-cords very clearly ; but 

 the right side of Vogt and Yung's fig. 276 is very nearly 

 interradial, and not radial as they state. If it were in the 

 axis of a radial, as they say, the nerve-cord would not end 

 abruptly, as they figure it, at the level of the " anneau penta- 

 gonal;" but it would be seen to pass on beyond this towards 

 the second radial, as is represented on the left side of fig. 267. 

 In like manner the left side of fig. 276, which would be inter- 

 radial according to their description, is almost radial. It 

 strikes one of the radial diverticula of the body-cavity into 

 the calyx (axial radial canals), wliicli is enclosed by a radial 

 process of the rosette, the same part which is lettered o, but 

 not explained, as I have already stated. Not only have the 

 Swiss authors entirely failed to understand the orientation of 

 their sections through the calyx, but they have altogether 

 neglected to give any account of the remarkable way in which 

 each radial receives nerves from two sources, while all the five 

 double nerves of the rays are connected among themselves by two 

 sets of commissures, interradial and intraradial, thus forming 

 the great pentagonal commissure which is lodged within the 

 substance of the first radials. It is true that they give a 

 nearly horizontal section through this commissure (fig. 264), 

 and speak of it as the " anneau pentagonal du systbme nerveux 

 central," but they say not a word about the manner in which 

 it is formed — a somewhat remarkable omission when we con- 

 sider its physiological importance ; while the mode in which 

 they refer to it is calculated to seriously mislead the unfortu- 

 nate student. 



They make the following statement on p. 523 : — " L'orien- 



* " On the Nervous System of Antedon rosaceus" Quart. Journ. Micr. 

 Sci. new ser 1884, vol. xxiv. pi. xxxv. fig. 1. 

 t Trans. Liun. Soc. 2nd ser. (Zool.), vol. ii. 1879, pi. viii. fig. 3. 



