

MONOGRAPH OF THE EXISTING CRIXOIDS. 



151 



or insect bodies united by the possession of a single head in common, from which 

 center five of the bodies, radiating outward, represent the five rays of the crinoid 

 while the sixth represents the column. 



The question which of the intcrmetameric divisions in the echinoderms rep- 

 resents the plane of union between the originally five and ojijxi-itf anterior and 



Fio. 92. LATERAL VIEW OF A YOUNG SPECIMEN or PTILOMETRA MACKOSEMA PROM SOUTHWESTERN AUSTRALIA, SHOWING THE 



CIRRI APPROACHING THE ADULT TYPE. 



posterior extremes of the body is of no concern in a discussion of the adult animals. 

 After the union of the two ends the body as a whole becomes truly and absolutely 

 radial, and any subsequent modification, no matter of what description, is based 

 or projected upon a fundamentally radial body. 



