Anatomical Nomenclature of Echinoderms. 
3 
cation which “ arises in the walls of the water tube,” thus 
giving a third meaning to the same term, while Agassiz, as 
we have seen, has used it in yet another sense. Is it too 
much to ask on behalf of the student of the future that it be 
employed in one sense only? In the following pages it will 
be used to denote the madreporic or stone-canal. 
2. Dorsocentral and Centro-dorsal. 
These two names are frequently used as if they were 
synonymous, though in reality they denote plates of very 
different morphological characters. 
The term u dorsocentral ” appears to have been first used 
by the Messrs. Austin * for that part of a Crinoid which was 
called the pelvis by Miller, i. e. the ring of plates which rest 
upon the top stem-joint. In some cases five separate plates 
may be distinguished, in others only three, while in others 
there seems to be but one undivided plate with a stem-facet on 
its lower surface ; and even this facet is absent on the central 
plate of Marsupites . Owing to the rapid spread of the 
Mullerian terminology, in which the lowest plates of the 
Crinoidal calyx were designated basals, the collective name 
u dorsocentral ” applied to them by Austin never found 
general acceptance. But in Loven’s classical work f on the 
Echini the term u dorsocentral system ” is used to denote 
the central plate in the apex of a young Urchin, together with 
the two rings of genital and ocular plates around it. He 
regarded the central plate of Marsupites as homologous with 
that of the Urchin, and also compared the ocular plates of the 
latter to the radials of Marsupites , two determinations which 
I fully accepted when writing on the subject in 1878 J, 
though I could not follow Loven in the other homologies 
which he proposed, nor in his views respecting the primitively 
compound nature of the dorsocentral plate. I suggested at 
the same time that the homologue of the latter was to be 
found in the terminal plate at the base of the stem in the 
stalked larva of Comatula , which I carefully distinguished 
from the enlarged upper stem-joint or centro-dorsal piece. 
Sladen § adopted this view in 1884, since which time the 
* u Descriptions of several new Genera and Species of Crinoidea,” 
Ann. & Mag. Nat. Hist. 1843, vol. xi. p. 196. 
t u Etudes sur les J^chinoidees,’’ Kongl. Svenska Vetenskaps-Aka- 
demiens Handlingar, 1874, Bd. xi. no. 7, p. 65. 
t “ On the Oral and Apical Systems of the Echinoderms,” Quart. 
Journ. Micr. Sci. 1878, vol. xviii. p. 359. 
§ u On the Homologies of the Primary Larval Plates in the Test of 
Brachiate Echinoderms,” Quart. Journ. Micr. Sci. 1884, vol. xxiv. p. 25. 
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