THE HYDROMEDUSAE 



FIG. 14. 



Fio. 15. 



11. Ocellus of Lizzia Koellikeri. oc, pigmented ectodermal cells ; I, lens. 



12. Otocyst of Phialidium. d 1 , superficial layer of ectoderm ; d 2 , deep layer of ecto- 

 derm ; h, auditory cells of ectoderm ; hh, auditory hairs ; np, nerve body ; Tir 1 , upper nerve 

 ring; r, endoderm cells of the circular canal. The otolith cavity is seen above h. (Fi^s. 

 11, 12, from Lankester, after Hertwig.) 



13. Otocyst of Euchilota. o, otolith ; remaining letters as Fig. 12. (After Hertwig.) 



14. Simple tentaculocyst of one of the Trachoniedusae (Rhopalonema velatmn). The process 

 carrying the otolith or concretion hi; formed by endoderm cells, is enclosed by an upgrowth 

 forming the "vesicle," which is not yet quite closed in. (From Lankester, after Hertwig.) 



15. Optical section of a cordylus or sense club ; the surrounding structures are only 

 roughly indicated. CC, circular canal; EU, exumbral surface; Me, mesogloea ; NR, the 

 outer, NR, the inner parts of the nerve ring; SU, subumbral surface; T, tentacle; V, 

 velum. (After Brooks.) 



