42 BULLETIN OF THE 



cally. If the former is a madreporite, the latter is not ; it the latter is 

 a madreporite, the former cannot be. What additions now take place ? 



(1) The genital grows arouud the opening of the madreporic tube. 



(2) The calcifications of the stone canal form. Neither of these events 

 makes (g 1 ) the first genital a homologue of the odontophore, the ho- 

 mology of which preserves its distinctness whatever occurs. 



In the case of the orals of Amphiura, it is found that one of them 

 grows around the madreporic opening in the same way that one of 

 the genitals grows in Asterias. It seems to me that this fact alone 

 does not make genitals and orals homologous, and does not prevent 

 the homology of orals of Amphiura and odontophores of Asterias.* 



A comparison of the odontophore with the oral of Amphiura was made 

 by Ludwig. According to Carpenter, he no longer holds that view, 

 although Carpenter does not say what plate in Ophiurans Ludwig now 

 regards as the homologue of the odontophore. As " interambulacrals 

 (marginals)" are wanting in Ophiurans (Amphiura), it is difficult to 

 interpret what plates here correspond with the unpaired marginals of 

 the starfish. Perhaps Ludwig might still consistently hold that while 

 the odontophore is an " Unpaare Interambulacralplatte," it is still a 

 homologue of the orals of Amphiura where no marginals like those of 

 the starfish are found. I believe that the first interbrachial (odonto- 

 phore) is homologous to the oral, but do not say that Ludwig now holds 

 such a view. 



Sladen holds that the presence of the madreporite in a plate does not 

 mean homology of that plate among Echinoderms.t It does not lie in 

 the genital in certain starfishes, and it is disconnected with the orals in 



* "Waiving the difference of opinion of Sladen and Perrier (Compt. Rend., Vol. 

 XCV., July 10, 1882), — the latter of whom holds that the madreporiform body in 

 Brisinga is always formed on one of the odontophores, and the former, that no 

 connection whatever exists between these two bodies, — is it not possible to con- 

 clude that we may have, in this ophiurid-like starfish, a genus in which the 

 odontophore, like the oral of an Ophiuran, has been modified by its proximity 

 to the madreporic opening, even if no connection has resulted ? 



t In this connection it may be well to call attention to the migration of the 

 madreporic opening in Echinarachnius along an interradius from the edge of the 

 disk towards the centre, as shown in my paper on the development of this Clype- 

 astroid (Bull. Mus. Comp. Zool., Vol. XII. No. 4). A. Agassiz had already shown 

 the migration of the periproct in the same genus (Bull. Mus. Comp. Zool., Vol. III. 

 No. 9, p. '295). The madreporite moves from the margin of the disk to the centre; 

 the periproct of Echinarachnius moves from the centre to the margin. It might 

 better he said in regard to the madreporite, that by the growth of plates about it 

 the madreporic body is pressed to the centre from the margin. 



