OF THE ADULT AURELIA. 



73 



sponded to the hydra-form condition, and infer that the whole 

 hydra became a medusa ; * in other words, that the hydra was 



* The individuality 

 of Hydro - Medusce. 

 Perhaps the diversity 

 of individuality is no- 

 where so extensively 

 exemplified as among 

 the Hydroida, nor 

 tends so strongly to 

 verify the belief in the 

 merely partial indi- 

 viduality of that por- 

 tion which is set free 

 by budding or fissi- 

 gemmation. It can 

 be shown that the 

 same individual stock 

 bears evidence in its 

 own person that what 

 at one time may ap- 

 pear to be a distinct 

 individual, at another 

 time is incontestably 

 the reproductive or- 

 gan. As instances of' 

 this kind, I will ad- 

 duce two of the most 

 characteristic forms of 

 reproduction that oc- 

 cur among Hydroids. 



Rhizogeton fusifor- 

 mis. Ag. The first 

 that I shall describe 

 is, in more than one 

 respect, one of the 



at 



Fig. 38. 



Fig. 38. Rhizogeton fusiformis. Ag. 20 diam. A marine Hydroid. I, A 

 sterile hydra; II, III, IV, fertile hydras, or reproductive organs; st, the stolon, 

 or creeping stem ; , point of junction of the upright stems with st ; ?n, the 

 mouth ; d, d l , the digestive cavity ; <, tentacles ; p, the parchmenty sheath ; p l , the 



