FIG. 3. Transverse 

 section through Sycon 

 gelatinosum from Parker 

 & Haswell, Textbook of 

 Zoology. 1C, incurrent 

 canal; R, radial tube 

 (flagellated chamber) ; 

 sp, triradiate spicules; 

 sp', spicules of cortex; 

 dc, cortex; sp", triradial 

 spicules of atrium; ec, 

 ectoderm; en, endoderm; 

 pm, external incurrent 

 pore; pp, prosopyle; ap, 

 apopyle; di, diaphragm; 

 exc, excurrent passage; 

 P. G., atrium; em, early 

 embryo; em', late em- 

 bryo. 



