306 



PHYLUM ECHINODERMATA. 



arranged. But the so-called genital opening has only been observed in a 

 few cases, and it may be that in the forms with pinnules the gonads were 

 in them. The identification of the other opening is too precarious to 



FIG. 213. Cysi.obla.stus Leuchtenbergi (after Volhorth, from Bather). 1 oral; 2 posterior; 

 3 aboral view; 4 analysis, with plates numbered. As anus;* anal interradius in 1; 

 M water-pore or generative opening; sp plates on the floor of the arm grooves; Sf 

 attachment of stem. 



allow of our drawing any inference as to the relative position of the 

 water-pore and anus, but when the madreporite can undoubtedly be dis- 

 tinguished, it is placed in the same interradius as the anus. 



The calcareous plates of Cystids often seem to be composed of three 

 distinct layers : a smooth and thin outer layer, the epistereom ; a thick 



A B 



.of 



o/n- 



FlO. 214. Aristocystis bohemicus. A, from the left side, B from the oral face (after Bar- 

 rande). 071 anus ; b mouth ; gtx generative opening ; rndp hydropore. 



