NOTES ON ECHINODERM MORPHOLOGY. 



381 



the basals of the Crinoid and the genitals of the Asterid or 

 Urchin, which have not been previously discovered in an Ophi- 

 urid. This latter point will naturally be denied by Ludwig, 

 who regards the genitals of an Urchin or Asterid as represented 

 by the orals of an Ophiurid or Crinoid, since they are all per- 

 forated by the primary water-pore of the larva. In the larval 

 Asterid the water-pore occupies the same position relatively to 

 the plate which it perforates, as in the Ophiurid and Crinoid. 

 Fig. Ill is a projection of the calyx of an Antedon larva as seen 



Fig. III. — Apical system of an early Crinoid larva, in which the radials (4) 

 are still very small. The stem-joints are represented as telescoped 

 into one another, so as to bring the terminal plate of the base of the 

 stem or dorsocentral (1) into close relation with the basals (3). The 

 course of the gut from mouth to anus {an) is indicated by the dotted 

 line and arrows, w.p. Water-pore. 



from the dorsal side when placed in the natural position of the 



situated outside the radials of Ophiopholis, are really the orals ; while the 

 latter, situated inside the radials of Aster acantJiion, are the genitals. Fol- 

 lowing Agassiz, I have wrongly described the former as genitals or basals 

 (this Journal, vol. xviii, p. 369), though his figure should have indicated 

 his error to me ; and I am sorry to say that this statement was reproduced 

 in the ' Comparative Embryology ' of my lamented friend, the late Prof. 

 Balfour (p. 469). As I did not notice the error till after reading over the 

 proof of the chapter on Echinoderms, I therefore take this opportunity of 

 correcting it. I believe, however, that basals are really present in Amphiura 

 squamata, though I should say that Ludwig expresses no opinion respect- 

 ing the homology of the plates discovered by him, and must not therefore 

 be considered as responsible for the views enunciated above. 



