PRIMARY LARVAL PLATES OP BRACHIATE ECHINODERMS. 39 



Brisinga, in which the madreporiform body is stated to be 

 always formed on one of the odontophores in that Starfish. 

 From this the conclusion is drawn that Brisinga occupies an 

 intermediate position between Asterids and Ophiurids. With 

 this statement I am unable to agree, as I do not find when a 

 section is made of the disk of Brisinga any connection what- 

 ever between the madreporite and the odontophore, the 

 former being merely superposed over the odontophore in conse- 

 quence of its own extreme position at the margin of the disk^ 

 and the prominence and size of the odontophore. No morpho- 

 logical relation exists whatever. The origin and mode of 

 formation of the odontophores in Brisinga which M. Perrier 

 describes are very remarkable. They are described as formed 

 from the plates of the proximal ring of interradial plates 

 which originally surround the dorsocentral plate, that is to say, 

 from the plates which we have designated basals (marked 3, 3) 

 in the preceding pages. " Les pieces interbrachiales sont aiusi 

 refoulees constamraent versle bord du disque; en meme temps, 

 elles se reduisent de plus en plus, vienneut se placer exactement 

 dans 1' angle des bras, cessent ainsi peu a peu de faire partie du 

 squelette du disque et finissent par constituer les odonto- 

 phores. Ainsi les odontophores sout les restes des pieces du 

 premier rangdu disque primitif de la Brisinga.^' ^ 



Arguing from the identity of the plan of organisation in 

 Brisinga and the true Asterids, Perrier concludes that the 

 odontophores are formed in a similar manner in the Starfishes 

 generally. From this conclusion I dissent entirely, for in none 

 of the Starfishes of which we know anything of the embryo- 

 losrical stages does such a transformation of basals into 

 odontophores take place. The two plates are separate and 

 distinct, and co-exist independently from their first formation. 

 In further support of this remark, 1 need only refer to the 

 large number of forms, briefly indicated in a preceding page, 

 in which the primitive interradial or basal plate remains pro- 

 minent and distinct even in the adult form. Furthermore, 

 believing as I do that the odontophore has its development in 



I 1. c, p. 63. 



