778 



CHAULKS L. BDULENGEU. 



tentacular nematocysts of the fully-formed medusa tlius arise 

 in the interstitial cells derived from the ectoderm of the 

 parent hydroid. 



The ocellar bulbs are, of course, retained throughout the 

 life of the medusa, and, as mentioned above, keep on supply- 

 ing the tentacles with stinging-cells ; they are no doubt 

 especially active during the regeneration of these organs. 

 This explains the constant presence of such swellings at the 



Text-fig. 5. 



vel 



--nerw 



IxevrL 



A longitudmal section of im ocellar bulb of Man-isia lyonsi 

 just before the development of a tentacle, vel. Velum, nem. 

 Small nematoeyst. i?e»i.^ Large nematocyst. 



bases of the tentacles of the Hydromedusas, as well as their 

 early appearance and relatively enormous size in the develop- 

 ing medusa-buds. The function of bearing the ocellar sense- 

 organs must be a secondary one, for such bulbs are conspicuous 

 in the formation of medusas which do not possess ocelli, e.g. 

 Podocoryne carnea, concerning which Goette (11, p. 19) 

 remarks : 



" Bald nach der Fertio-stelluns: des Velum verdickt sich 

 das Ectoderm jedes Eandwulstes dicht iiber dem Yelum zu 



