ZOOLOGY OF THE IXVERTEBRATA. 



303 



We will now pass on to Chapter XV. and take an example 

 from the Echinodermata, which are divided into five classes, viz. : 

 Asteroidea, Ophiuroidea, Crinoidea, Echinoidea, and Holothu- 

 roidea. From the last of these we have selected. 



^'g- 79- — View of the internal organs of a Holothurian, which has 

 been cut open along the middle dorsal line. From Leuckart. 



