NOTES ON ECHINODEKM MORPHOLOGY. 385 



rite in these young Starfishes relatively to the rudiment of the 

 so-called *' odontophore/' which Ludwig considers to be homo- 

 logous with the orals (mouth shields) of Ophiurids.^ In Brisinga 

 this plate bears the madreporite ; and I cannot understand how 

 Ludwig, knowing this fact and regarding the " odontophore^' as 

 an oral plate, can have framed his theory of the homology of the 

 orals of Ophiurids with the genitals of Asterids (including 

 Brimiga). According to Perrier's observations^ on the young of 

 this genus there are large interradial pieces separated from the 

 dorsocentral by smaller plates. They are constantly pushed 

 towards the margin of the disc, become reduced in size, and 

 eventually constitute the odontophores, one of them bearing the 

 madreporite. Novv^ Ludwig, for other reasons, considers the 

 odontophores of Brisinga, and the Asterids generally, as homo- 

 logous with the orals of Ophiurids and Crinoids, and their relation 

 to the madreporite supports that view. How, then, can these 

 last be also homologous with the genitals of the Asterids, as his 

 theory asserts ? Must not the genitals of Brisinga be sought for 

 among the smaller plates between the future odontophores and 

 the dorsocentral, just as in the Ophiurids (figs, i, ii, 3) ? It is 

 hardly likely that the odontophore of an ordinary Asterid is 

 primarily an oral, while that of Brisinga is a genital. Does not 

 Brisinga represent an intermediate stage between ordinary As- 

 terids with large genitals (basals) and Ophiurids with large orals 

 and small basals ? 



In the Ophiurid (figs, i, ii) the proximal ring of interradial 

 plates (basals) is quite insignificant in character, and only deve- 

 lopes late, long after the appearance of the radials. These are 

 at first in immediate contact with the dorsocentral, so that there 

 is room between them and the edge of the disc for the orals, 

 which are next the radials in order from the abactinal centre j 

 and as far as can be judged from the figures of Agassiz and 

 Ludwig, they appear to develop before the water-pore which 

 pierces them from the first. 



Lastly, in the Crinoid (fig. iii) the basals appear early, and so 

 do the orals which rest upon them, but the radials which ulti- 

 mately separate the two rings are only developed much later ; so 

 that here again the orals are quite close to the abactinal centre, 

 and therefore to the water-pore. 



One result of Ludwig's theory is to give the dorsocentral 



1 I use the word " odontophore " for convenience sake, though I fully 

 agree with Ludwig's strictures on the name. But it is at any rate better 

 than "Erstes intermediare Interambulacralstiick." If it represents the 

 mouth-shields of Ophiurids and the orals of Crinoids, why not call it an 

 oral at once ? 



2 "Note sur les Brisinga,'' ' Comptes Rendus,' t. xcv, pp. Gl-63. 



