CR1NOIDEA. 



263 



The generative organs are therefore not placed within the 

 calyx, and it follows of necessity that there is no generative 

 opening or " ovarian aperture " in the walls of the calyx. 

 The ventral surfaces of the arms and pinnulse are furnished 

 with grooves, which in the living species are seen to be 

 covered with vibratile cilia. The brachial grooves coalesce 

 till they constitute five (sometimes fewer) primary grooves, 

 which are continued from the bases of the arms to the mouth. 

 The action of the cilia gives rise to a constant current of sea- 

 water, bearing organic matter in suspension; and this current 

 proceeds from the brachial grooves to the mouth. In this 

 way the animal obtains its food. As the bases of the arms 

 are separated from the mouth by an intervening space, it 

 follows that the brachial grooves are continued over the 

 ventral surface of the calyx, till they reach the oral opening. 



Fix. 152. Platycri-nus tricontadactylus. Carboniferous. The left-hand figure shows the 

 f-alyx, arms, and upper part of the stem, and the figure next this shows the surface of one of 

 the joints of the column. The right-hand figure shows the proboscis. 



There is no doubt that it is by the above arrangement that 

 the living Crinoids obtain their food, and the mechanism 

 seems to have been essentially the same in many extinct 

 species. In the Palaeozoic Crinoids,, however, there seems to 



