232 LE. Billings on the structure of Crinoidea, Cystidea, ete. 
8. On the occurrence of Embryonic forms among the Paleozove 
Echinoderms. 
Fig. Bi tae asterigera Sars, —_? from mag 
ler). e ‘the stomac h; 0, part of the "bo dy of the larv: 
C, ambulacral centre, position of the permanent mouth, i 
ot open ; d, one of the five ambulacral canals ; 
e, san , madreporic plate; m, entrance into the 
stomach ; 0, cesophagus; p, larval — or pseudostome ; 
T, Cesop: ring; v, vent. 9. al figure described 
below. 10. Codonites stelliformis, sbunas ad to show 
both body and summit. 11. Summit of fig. 
No proposition in Natural History has been more clearly 
demonstrated than this:—That, in general, the paleozoic ani- 
mals resemble, both in external form and internal structure, the 
embryonic stages of those of the same class at present existing. 
Prof. Agassiz has long taught in his lectures and various pub- 
_lications, that this is especially observable in the Kchinodermata. 
Ju udging from the figures and descriptions of Miller, Agassiz, 
Thomson, Carpenter and others, I should say, that in this class, 
the most oicarge! resemblance is that which occurs between the 
n 1 h 
subjects dis¢ussed in these notes, is, that in all four of these 
groups, the mouth is situated in one of the interradial areas 
not in the ambulacral center, as it is in the adult forms of the 
existing Echinodermata. 
naria asterigera Sars, according to Miiller, the digestive 
cavity is a sub-globular sack without any extensions into the 
rays, as there are in the adult Star-fishes. The oesophagus, fi 
8, 9, isa fleshy, consistent bb, with a large mouth or pseudos- 
ing somewhat at dra Rey — mouth, and situated in one 
of the interradial The madreporie plate, f, and 
sand canal, e, the ‘aie telat the convoluted pists (when it 
