lie 



at, 



»t 



- 



in 



wit 



a- 



HYDROZOA. 



U 



In. 





link 



t: 



■.- 



a? 



11 



m 



in-,, 

 them 





pr 



i; 



in 



til 



< . 



1$ 



67 



tive organs ; thus eventually becoming similar to 

 the huge reproductive body, from whose fertilised 

 ovum the primitive Hydra-tuba was produced. 

 This, and the stock which it developed, does not 

 however, perish, but may again, by growth and 

 fission, give rise to fresh successions of generative 

 bodies. 



Fig. 15. 



Development of Chrysaora : — a, ova, with gelatinous invest- 

 ment, from Chrysaora hysoscella ; b and c, free ova ; d, young 

 Hydra-tuba, with four marginal tentacles, developed therefrom* 

 e, the same, with eight tentacles ; /, Hydra tuba, in its ordinary 

 condition ; g, another Hydra-tuba, marked with constrictions ; 



form 



Unlil men un( *ergoing fission, in which the tentacles are seen to arise 



teDb fr0m bel ° W the constricted ' portion, while its upper segments 



separate, and become free-swimming zooids (k\ 



ieir' v J 



Similar to the above appears the life-history of 



different structure of the detached reproductive 

 zooids which these genera present. On the de- 

 velopment of Rhizostoma itself accurate observa- 



J 1 • 



tions are wanting. 



In the Lucernariadce proper, no free zooids are 

 produced, but the generative elem ents are formed 



f 2 



