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

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

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

 spicules of dermal cortex (dc) ; sp" , tetraradiate spicules of gastral cortex {gc); 

 ec, ectoderm; £«,endoderm; pin, pore membrane ; pp, prosopyles; ap y apopyle ; 

 di, diaphragm; exc t excurrent passage; PC, paragastrlc cavity; em, early 

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

 the sponge 



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