E. Billings on the structure of Crinoidea, Cystidea, etc. 238 
oceurs), are situated above the orifice, m, and between it and the 
ambulacral center, c. The circular space atc, is undoubtedly 
the homologue of the central space in the apex of Nucleocrinus, 
figs. 8 and 5, and of Codonvies, figs. sit and 11. It is also the 
water, and drawn i he es sack mE the mouth 
and cesophag by athe” action of interradial cilia. I believe 
that all the ossil Crinoidea, Blastoidea and Cystidea, ingested 
their food in this way, and without any aid whatever from the 
arms or pinnu 
- Perhaps there is no embryologist who will not admit, that it 
is possible for an animal like Bipinnaria to develope organs of 
reproduction and propagate 27 species, none of its other parts 
making any farther advance uch an animal, with some 
even with the surface, the swimming appendages aborted, and 
the vent closed up, it would resemble the cup of an Actznoer?- 
nus, fig. 9,a. The lateral orifice would then be both mouth 
and vent, as it is, at first (according to Prof. A. Agassiz, Seaside 
Studies, p. 125), in the embryo of Asteracanthion Berylinus. 
The ambulacral shale of Bipmnaria are the homologues, in 
a general way, of those which are found beneath the vault of 
Actinocrinus, and extend out into the grooves of the arms. If . 
the ventral perisome of the Crinoid were to be removed (the. 
internal organs remaining undisturbed) the arrangement dis- 
closed would be that represented in fig. 9,—a convoluted plate 
in the center with the canals radiating from it. The most strik- 
ing difference is the absence of the cesophageal ring. Accord- 
ing to the organization of Actinocrinus there could be no 
cesphagus at that point, and consequently there is no ring. The 
convoluted plate represents the ma ric apparatus. one 
sucking feet of the Star-fish, — probably, represent the 
spiratory tentacles that border the grooves of the Be ncds, sak 
modified into prehensile and rea actly organs. Bipinnaria 
ese two characters 
embryonic and Conese, a the Star- fish, but they were perma- 
nent in most paleozoic 
In ites stelliformis EFesicastas stelliformis Owen and 
Shumard), figs. 10, 11, the ambulacral ce poem: c, is completely 
Am. Jour. Sci.—SEconD vines, Vou. L, No. 149,—Sepr., 1870, 
15 
