88 



SYSTEMATIC ZOOLOGY 



animal (Fig. 76), which can thus move about from place to 

 place, but even here a stalk is present in the larva. At the free 



end of the stalk is the cup or 

 calyx, provided with the oral 

 disc on its upper surface, the 

 mouth being near the center, 

 and on the same surface is 

 the anus, excentrically placed. 

 Surrounding this disc are the 

 arms, which at their point of 

 origin are five in number, radi- 

 ally arranged, and as they 

 usually branch dichotomouslv, 

 there are many more at the 

 tips. The arms are supported 

 by skeletal plates arranged 

 end to end, and from each 

 plate a short lateral branch 

 is given off ; these lateral 

 branches are called pinnulae, 

 — they suggest the barbs on 

 a feather. At the mouth 

 five grooves arise, which pass 

 radially across the oral disc 

 and along the oral surface of 

 each arm, dividing as the arms 

 divide ; these are the ambu- 

 lacral grooves, and they are 

 provided with hollow tentacles 

 which are a part of the water 

 vascular system, and thus cor- 

 respond to the tube feet. 



The Crinoidea are often at- 

 tractively colored, occurring in 

 white, purple, yellow, and 

 brown. Of their development 

 we know but little. The sexes are separate, and in those species 

 whose development has been observed a bilaterallv symmetrical 

 larva, more or less ciliated, is produced. This class possesses 



Fig. 75. Metacrinus interruptus. A stalked 

 crinoicl. (After Carpenter, from Parker and 

 I [aswell's Manual.) 



