MONOGRAPH OF THE EXISTING CRINOIDS. 



133 



Originally the echinodermal skeleton consisted merely of scattered calcareous 

 deposits in the mesoderm, chiefly in the body wall, probably in the shape of spiculcs 

 and small plates comparable to the less speciali/ed 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 VIEW or A SPECIMEN OF COMATULIDES KECAMEROS FROM SOUTHWESTEKN JAPAN, SHOWING THE RELATIVE 



PROPORTIONS OF THE ARMS, PINNULES, CENTRODORSAL AND CIKRI. 



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

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



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

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

 within constantly narrowing limits. 



