MUSEUM OF COMPARATIVE ZOOLOGY. 41 



— viz. terminals, dorsocentral, genitals, spines, and even ten of the oral 

 ambulacrals — have appeared before there is any calcification about 

 the terminal opening of the madreporic tube. Does not this fact call 

 for extreme caution in regard to statements that would lead us to ho- 

 mologize the madreporic plate with a genital rather than any other 

 Asterid plate] Another thing, the outer edge of the genital grows 

 around the end of the madreporic body to enclose it, and the stone 

 canal forms before there is any cribriform plate over the opening. 

 There is yet one fact which ought to be taken into consideration with 

 those mentioned ; viz. four interbrachials (odontophores) form at first, 

 and the lower end of the madreporic canal occupies the homologous 

 position of the fifth. "While this fact does not demonstrate the ho- 

 mology of the madreporite, it is thought to have a bearing on the 

 subject. The madreporite is not in intimate union with the odonto- 

 phore after the odontophore forms, but it lies in the same inter- 

 radius.* I venture to say that, if it is not in some kind of connection 

 with the odontophore in Asterias, as Perrier says it is in Brisinga, it cer- 

 tainly is very close to it. 



Sladen {op. cit.) finds no morphological relation between the odonto- 

 phore and madreporite in Brisinga. While we may or may not subscribe 

 to Sladen's criticisms of Perrier, he does not in either case seem to me 

 to prove that there is " no morphological relation" between madreporite 

 and odontophore, for when we go to very young stages in the growth 

 of Asterias, we find a very intimate connection between the madreporite 

 and odontophore. 



As all the other odontophores of Asterias form on the actinal hemi- 

 some, and the plate which occupies a similar position in the interradius 

 has a like position of origin, it would seem that Brisinga differs very 

 considerably from Asterias, as far as the formation of the madreporite is 

 concerned. In my specimens I certainly detected the odontophore of 

 the interradial in w T hich the madreporic body is found on the actinal 

 hemisome, in the same relative position as the other odontophores. At 

 the same time the genital (g 1 ) had not grown around the opening of 

 the madreporic tube. Here, then, were two separate plates on opposite 

 ends of an axis of the body. One could not be the other morphologi- 



* Obviously, from the fact that one of the genitals grows around the madre- 

 poric opening, we are not obliged to regard this genital itself as homologous with 

 a madreporite. We might easily suppose the primary separation of the madreporic 

 opening and this genital much greater, and the stone canal so reduced that the 

 madreporic body occupies a position which it is said to have in Brisinga. 



