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

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

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

 spicules of dermal cortex (dc) ; ./", tetraradiate spicules of gastral cortex (gc); 

 ec, ectoderm; en, endoderm; /./, pore membrane; /)/, prosopyles ; ap, apopyle ; 

 di, diaphragm; exc, 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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