358 



p. HERBERT CARPENTER. 



occupying the centre of the dorsal pole of the calyx of Mar- 

 supites (tig. Ill, 1) is regarded by him, as by Milller, as 

 composed of five closely anchylosed basals, and as homo- 

 logous with the central disc of the apical system in the 

 Echini (fig. ii, 1). 



Fig. III. — Apical system of Man^ipUes. 1. Central disc = basis 

 (Lovea). 2. Under basals ^ first parabasals (Loven). 3. Basals 

 = second parabasals (Loven). 4. Radials. 



The five genital plates (fig. it, 3, 3) which are in close 

 contact with this subanal plate in the Echini, are regarded 

 by Loven as homologous Avith the similarly situated plates 

 forming the first or proximal ring in the Ma7'siq)ites calyx 

 (fig. Ill, 2, 2). I would, however, venture to suggest that 

 Loven is mistaken in this view. The genital plates of the 

 Urchins are interradial in position, while the plates of the 

 proxiaial ring in ^larsujjitcs are radian// disposed. This 

 fact seems to me to be a conclusive proof that the two sets 

 of plates, although similarly situated with regard to the 

 central plate of the Apical system, are in no May homologous, 

 as supposed by Loven, but merely analogous. 



Comparisons such as these, which are made without any re- 

 gard to the positions of the parts compared, with reference to 

 the general radial symmetry of the Echinoderm type, appear 

 to me to be quite erroneous. Loven would, I am sure, be the 

 first to admit this, and I imagine that he has fallen into this 

 error from having inadvertently overlooked the relative posi- 

 tions of the ])lates in the first and second rings around the 

 central disc of Marsiqntcs (fig. in, 2, 2, 3, o). 



The plates of the second ring are situated interradially, 

 and I believe them to be truly homologous witli the genital 

 plates oi Echini (fig. ii, 3, 3), which occupy a similar inter- 

 radial position. Loven, however, considers that they have 

 *' no analogue " in the Urchins, nor in the other Crinoids, a 



