I2O 



ANNULOIDA. 



fore, not placed within the calyx, and it follows of necessity 

 that there is no generative opening or "ova- 

 rian aperture " in the walls of the calyx. 

 The ventral surfaces of the arms and pin- 

 nulae are furnished with grooves, which 

 in the living species are seen to be co- 

 vered with vibratile cilia. The brachial 

 grooves coalesce till they constitute five 

 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 mat- 

 ter in solution ; 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 



Fig. 73. Platycrinus tricontadactylus. Carboniferous. The left-hand figure shows 

 the calyx, 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 ; and 

 above is a magnified figure of part of one arm with its pinnulae. 



continued over the ventral surface of the calyx, till they reach 

 the oral opening. 



