352 



p. HERBERT CARPENTER. 



larva, though in some fossil Crinoids there is a single plate 

 in the centre of this ring, as in the Apical system. Further, it 

 is by no means so constant in its appearance as the Apical 

 system, and often undergoes more or less resorption before 

 maturity is reached. This is the case even in some of the 

 Crinoids, in which group this Oral system seems to reach its 

 fullest development. 



It is characteristic of the larval stages of existing Crinoids, 

 and in some cases persists through life, while it is very 

 highly developed in many extinct genera, more particularly 

 those of the earlier geological periods. 



The Oral system is consequently of considerable interest 

 from a phylogenetic standpoint, and adds another piece of 

 evidence to the many which we already possess, in support 

 of the view that the Crinoids represent an earlier stage in 

 the phylogeny of the Echinoderras than any other members 

 of the order. 



The component elements both of the Apical, and of the 

 Oral systems are better represented in the Pentacrinoid stage 

 of the development of Antedon, than in the larval or adult 

 condition of any Echinoderm with which I am acquainted. 

 It will be well, therefore, to take the Pentacrinoid as a 

 starting point, from which we can pursue our study of the 



erf-— 



Fig. I. — Calyx of the Pentacrinoid larva of Antedon rosacea. (After 



AUman.) st. Upper part of stem. cd. Centrodorsal piece = Top 



stem-segment. or. Oral plates = Interradials (Allman). 3. Basal 



plates. i. First radials. 



N.B.— In this and tbe following figures, the plates 3, 3, the position of 



which is inierradial with regard to tbe general symmetry of the Echinoderm 



type, are shaded for the saKc of distinctness. 



