136 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



tion by the echinoderms of the sessile habit; and the assumption of the sessile 

 habit went hand in hand with the modification of the skeleton in the direction of 

 the type common to similarly inactive forms, such as sponges and alcyonarians. 



FIG. 83. LATERAL VIEW OF A SPECIMEN OF EUDIOCRINUS JTJNCEUS FROM THE LESSER SUNDA ISLANDS, SHOWING THE 

 RELATIVE PROPORTIONS OF THE ARMS, PINNULES, CENTRODORSAL, AND CIRRI. 



Thus, as we understand it, the echinoderm skeleton considered strictly as the 

 echinoclerm skeleton was from the first a skeleton of the spicular type, the counter- 

 part of the skeleton of certain sponges and alcyonarians; but in reality this spicular 

 echinodermal skeleton is not an original development like the spicular skeleton of 



