EXPLANATION OF PLATES. 



Wherever the skeleton is shown in relation to the soft parts it is repi'esented by uniformly 

 dotted areas. The ectoderm is usually indicated 1)V the conventional columnar epithelium, the 

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

 magnification, as in PI. 1, fig-s. y-(), the calicoblast layer is usually not indicated, the mesoglo'a 

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

 conventionality represented by small processes from the face of the mesoglu»a. The orders or 

 cycles of mesentei'ies and septa are denoted by Roman numerals. 



REFERKNOE LETTERS ON THE FIGURES. 



cal calicoblast layer. 



cal. w calicinal wall. 



col. w column wall. 



d directives. 



des. pr (lesmoidal jirocesses. 



disk disk. 



ect ectoderm. 



ect. m ectodermal muscle. 



end endoderm. 



end. m endodermal niu.-<clf. 



en. t entotentacle. 



ex. t exotentacle. 



gr. gl granular gland cells. 



m mesentery. 



m. fll mesenterial filament. 



mes mesogUea. 



m. end mesenterial endoderm. 



nem. bat nematocyst battery. 



nr. 1 nerve layer. 



ov ovum. 



o. a oral aperture. 



r. ect reflected ectoderm. 



r. m retractor muscle. 



Sep. inv septal invagination. 



sk skeletotrophic tissue. 



ak. ect skeletotrophic ectoderm or 



calicoblast layer. 



sk. end skeletotrophic endoderm. 



sk. mx skeletal matrix. 



sper spermarium. 



sph. m sphincter muscle. 



st stomodicum. 



sup. can superficial canal. 



syn synapticulum. 



t tentacle. 



zoox zooxanthel la. 



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