MONOGRAPH OF THE EXISTING CRINOIDS. 



133 



Originally the ecliinodermal skeleton consisted merel_y of scattered calcareous 

 deposits in tlie mesoderm, cliiefly in the body wall, jirobably in the shape of spicules 

 and small plates comparable to the less specialized types of spicules and plates 

 found in certain holothurians (fig. 69, p. 127; compare figs. 543, pi. 4, and 569-571, 

 pi. 7) and in localized situations in species belonging to all the other groups, and 



Fig. 80.— Dorsal \tew of a .specimen of CoMATtruDES decameros from southwestern Japan, showing the beutive 



PROPORTIONS of THE ARMS, PINNVLES, CENTBODORSAL AND ClRBl. 



later of more or less fenestrated plates comparable to the so-called perforated 

 plates occurring in the MolpachidfC (fig. 70, p. 127). 



Fusion of spicules, and of sjiicules and plates, then occurred whereby the diverse 

 original elements were united into large skeletal units, each with a definite form 

 withia constantly narrowing hmits. 



