238 £. Billings on the structure of Crinordea, Cystidea, ete. 
) 
mentary particles; the most common recognizable forms being the 
horny casings of Enromosrraca or of the larve of higher Crus- 
TACEA.” (Op. cit., p. 700). 
The existence of large cilia within the intestinal canal, capa- 
ble of producing a powerful indraught of water, renders any 
acephalous mollusca. The indigestible particles would be, 
through the mouth, just as a 
Star-fish or a Zoophyte frees itself of the refuse portions of its 
food, by casting it out of the same aperture through which it 
entere 
10. On the Theory that the ambulacral and ovarian orifices are 
the oral apertures. 
Assuming that the four objections above noticed are sufli- 
cient to prove that the aperture which I call the mouth is not 
that organ, it is contended that the Cystidea, Blastoidea and 
Palzeocrinidea ingested their food through their ambulacral and 
ovarian orifices. This appears to me in the highest degree im- 
probable. In the recent Crinoids the grooves of the arms are 
occupied by four sets of tubes, which Dr. Carpenter calls the 
coeliac, the sub-tentacular, the ovarian and the tentacular canals. 
