GENEllAL MORPHOLOGY OP THE GROUP. 
Bch, 3 
General Morphology of the Group. 
This important subject is still being admirably and fully discussed, 
and the researches of Ludwig & Carpenter appear to be of very high im- 
portance; "Viguier has applied his observations to the practical purpose 
of systematic zoology. 
Ludwig (14) gives a preliminary notice of his later studies ; these have 
led to the following, among other, conclusions : — 
(1) The stalked larva of Antedon has, primitively, onlj^ one stone-canal 
and only one pore; they have the same relation as in the A steroidea — lying 
in the same inter-radius, and in the one next to that which is occupied by 
the anus. 
(2) In all save the Ophiuroidca^ the enteric tract coils from left to right. 
(3) The blood-vascular system of the Opliiuroidea presents the same 
relations, typically, as in the Asteroidea or Echinoidea ; an ab-oral ring, 
which lies partly under the radial shields, and which is homologous with 
the dorsal ring of Asteroidea and Echinoidea^ has been discovered. 
(4) The oral shields of the Ophiuroidea, and the oral plates of the 
Crinoidea are homologous with the genital plates of the Echinoidea and 
Asteroidea. 
The following are the chief results of Viguier’s comprehensive investi- 
gation into the skeletal characters of the Asteroidea (see also infra) ; ho 
insists on the value of the skeleton as an aid in classification ; the mouth 
is limited by a number of pieces, some of which, derived from the ambit- 
lacral and ad-ambtilacral series, are paired ; there is also an azygous “ odon- 
tophore.” The ambulacral or ad ambulacral ossicles may project furthest 
into the mouth. The “ odontophore is regarded as being hottiologous 
Ivith the peristomial plates of Eimjale, and with the Corresponding parts 
in Ophiurids ; a comparison is instituted between the “ teeth ’’ of the 
dentate Echinoidea, and the odontophore ” of the Asterid. As against 
IlfEckers “ Corm-theory ” he insists that there is no regular segmentation 
in the general Asterid skeleton, and that the radial coeca are not divided 
in correspondence with the segments of the body as they are in all 
Annelids. 
Ludwig (13) criticises ViguiCr’s views, especially insisting on the fact 
that only one ad-ambulacral piece (and not two) bounds every sucker 
(with the two ambulacral pieces) ; he holds very strongly that the 
“ tooth ’’ belongs to the ambulacral and not to the ad-ambulacral scries, 
lu the same paper, he takes occasion to state that ho has found in Astro- 
Xdiytonarhoresccnso more extended metamorphosis of the constituent parts 
of the peristome thau has been observed in any Ophiurid. 
The second part of Carpenter's essay (7) [see Zool. Hoc. xv. Ech. p. 4] 
should bo consulted by all who arc interested in the morphology of this 
group ; it is too condensed to be usefully abstracted. 
Stewart (25) has made the important observation that in the Cidaridm 
there are beneath the outer forked extremities of the five compasses, five 
diverticula of the chamber that occupies the interval betAveen the jaws 
and their muscles ; Avater would seem to enter the interior bf these' 
