EXPLANATION OF PLATES. 



Wherever the skeleton is shown in relation to the soft parts it is represented l>y uniformly 

 dotted areas. The ectoderm is usually indicated by the conventional columnar epithelium, the 

 mesogkea by a black line, and the endoderm as a tinted layer. In sections drawn under low 

 magnification, as in PI. I. figs. 2-6, the calicoblast layer is usually not indicated, the mesogkea 

 appearing to rest directly upon the skeleton. The retractor muscle on the mesenteries is 

 conventionally represented by small processes from the face of the mesogkea. The orders or 

 cycles of mesenteries and septa are denoted by Roman numerals. 



REFERENCE LETTERS ON THE FIGURES. 



cat calicoblast layer. 



cal. w calicinal wall. 



col. w column wall. 



d directives. 



dcs. jir desmoidal processes. 



disk disk. 



ect ectoderm. 



ect. in ectodermal muscle. 



end endoderm. 



end. m endodermal muscle. 



en. t entotentacle. 



ex. t exotentacle. 



gr. gl granular gland cells 



m mesentery. 



in. fil mesenterial filament. 



1 1 ies mesogkea. 



m. end mesenterial endoderm. 



nem. bat nematocyst battery. 



lir. 1 nerve layer. 



ov ovum. 



ii. a oral aperture. 



r. ect reflected ectoderm. 



r. in retractor muscle. 



sep. inv septal invagination. 



sk skeletotrophic tissue. 



sk. ect skeletotrophic ectoderm or 



calicoblast layer. 



sk. end skeletotrophic endoderm. 



sk. nix skeletal matrix. 



sper spermariuin. 



sph. m sphincter muscle. 



st stomodseum. 



sup. can superficial canal . 



syn synapticulum. 



t tentacle. 



zoox zooxanthel la. 



599 



