1870.] BILLINGS ON CRISTOIDEA AND BLASTOIDEA. 197 



ornatus, was a polystome animal, and drew in its food through its 

 six ovarian apertures, the large valvular orifice being the anus. 

 To me this appears uterly incredible. 



In fis;. 14 I have represented the mouth of Leshia mirahilis 

 Gray, Both Dr. J. E. Gray and Prof. Loven have pronounced 

 this aperture to have the structure of the valvular orifice of the 

 Cystidea. I have not the slightest doubt whatever but that the 

 mouth of the Cystideans foreshadows that of the Sea-urchins. 

 There is nothing whatever in its structure to show that it is nob 

 the mouth but the contrary. 



The new theory is not founded upon any peculiarities in the 

 structure of the ambulacral orifices, which would show that they 

 are oral apertures, but only upon the four objections above 

 noticed. The first of these is not logical, while at the same time 

 it is purely theoretical, and avails nothing against material and 

 visible facts. The fourth is completely disposed of by Dr. 

 Carpenter's observations, which prove that in the Crinoidea the 

 arms have no share whatever in the ino-estion of food. Tho 

 second and third objections are the same in substance, i. e., accord- 

 ing to the second the supply of water to the mouth, is diminished 

 by the occurrence of a Platyceras over it, while, according to the 

 third, the same effect is produced by the small size of 

 the aperture itself in some instances. It does not require 

 much consideration to convince one, that if these two objec- 

 tions are fatal to my views, they are equally so to the opposite 

 theory. In G. stelUformis, for instance, the pores through which 

 we must suppose the ovarian tubes issued from the interior are 

 only large enough to admit of the passage of a fine hair. They 

 are scarcely visible to the naked eye. The tube, under any 

 circumstances, must have filled them entirely. If any space at 

 all were left for the passage of a stream of water through the 

 pore by the side of the tube it must have been exceedingly 

 minute. 



When weighed as above, therefore, the evidence gives the 

 following results : — The first and fourth objections avail nothing. 

 The second and third militate against both theories. But 

 when we take into account that in no instance in the existing 

 Echinodermata, where ovarian pores occur, are they at the same 

 time oral orifices, the balance seems to be in favour of my view. 

 This is all I desire to say upon the subject at present. Although 

 I now firmly believe that the valvular orifice in the Cystidea, the 



