460 



CHARACTERS OF INVERTEBRATE ANIMALS 



e.g. in many ferns, where a central axis supports a row of leaflets 

 on each side in a feather-like 

 way. The mouth is in the 

 centre of the upturned disc, 

 and from it radiate five ambu- 

 lacral grooves, corresponding 

 to the similarly -named struc- 

 tures in a star-fish (p. 451). 

 As the arms branch, so do 

 these grooves, and their small- 

 est subdivisions run along the 

 pinnules. Projecting from each 

 side of an ambulacral groove 

 and its branches are a series 

 of delicate pointed structures 

 representing the tube-feet of a 

 star-fish, but here no longer 

 having anything to do with 

 locomotion. The intestine 



UT.ARM 



NALAPERTURE 



Fig. 282. Sea-Lily (Pentacrinus) 



A, Calyx and part of stalk (reduced). B, Upper side of 

 calyx, with arms cut off. 



opens near the mouth upon a 

 projection situated in one of 

 the interradial spaces. The 

 ander side of the cup is sup- 

 ported by regularly-arranged 

 circlets of calcareous plates, 

 some of which are compar- 

 able, it would appear, with 

 the apical disc of a sea-urchin. 

 There is, however, no madre- 

 porite. The under side of 

 each arm, arm -branch, and 

 pinnule is also supported by 

 a series of hard parts, jointed 

 together, however, so as to 

 permit of a certain amount 

 of movement. The stalk 

 upon which the animal is supported is five-sided, and it is sup- 

 ported by a series of calcareous pieces, in the form of prisms 



Fig. 283. Feather-Star (Comatula), climbing 



