19 



HYDROZOA 



10. Geryonia. One of the Trachy medusae, no hydroid phase. Long manubrium ; six radial 

 canals ; six tentacles ; velum. 



11. View of part of margin of disc of Geryonia showing tentaculocyst. 



12. Transverse section through the edge of the disc of Geryonia. (High power.) 

 Thickened ectodermal ring ; velum ; tentaculocyst ; n. i upper, n. 2 lower nerve-rings ; circular canal 



sub-umbrellar ectoderm ; gelatinous tissue. 



