Fig. 36. — Sycon gelatinosum. Transverse section through the wall of a cylinder 

 (parallel with the course of the canals), showing one incurrent canal (IC), and 

 one radial {R) throughout their length; s/>, triradiate spicules; sp' , oxeote 

 spicules of dermal cortex {dc) ; sfi" , tetraradiate spicules of gastral cortex {gc)\ 

 ec, ectoderm; eft, endoderm ; pjn, pore membrane ; pf>, prosopyles; ap, apopyle ; 

 di, diaphragm; e.xc, excurrent passage; PC, paragastric cavity; em, early 

 embryo; em' , late embryo- The arrows indicate the course of the water through 

 the sponge. 



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