ECHINODERMATA 



549 



abo 



abo 



aho ^ ^^' 



abo 



abo 



^or 



^f% 



Fig. 409. Diagrams to show the relative extent of the oral and aboral sur- 

 faces, and to compare the form of body, in the several classes of the Echino- 

 dermata. All the diagrams are in the same morphological position. From 

 Borradaile. i, Asteroidea. 2, Ophiuroidea. 3,*Echinoidea. 4,Holothuroidea. 

 5, Crinoidea. abo. aboral surface; or. oral surface. 



Fig. 410. Representatives of classes of the Echinodermata, in their natural 

 positions . A, A starfish (Asteroidea) . B , The shell of a sea urchin (Echinoidea) . 

 C, A holothurian. D, A sea lily (Crinoidea). 



