ALTERNATION OF GENERATIONS. 127 



of its own system. That is to say, as all these structures 

 are admitted to be strictly homologous, the large and 

 elaborately organized Medusae, instead of ranking as the 

 typical forms of their species, must be reduced to the level 

 of their humbler representatives in the Hydra fusca, and 

 regarded as mere spermatic and ovarian appendages, which, 

 like the staminiferous flowers of the Valisneria, accomplish 

 their special function after being detached from the parent 

 organism.* 



It is in farther support of this view, that in other Lucer- 

 nariada including the genus Lucernaria itself no medu- 

 soids are thrown off, but the ova and spermatozoa are 

 formed in immediate connection with the polypoid stock, 

 which, as being the only form in these species, must be 

 taken as the characteristic type of the group. 



But, besides such analogical arguments, the contrast be- 

 tween the permanence of the polypiform, and the evanes- 

 cence of the medusiform state, already noticed, as an argu- 

 ment for the typical character of the former, applies with 

 quite as much force to these Lucernarian polypes as to 

 those of the Corymform and Sertularian groups. The 

 " Hydra Tuba," indeed, is often spoken of as the " larva" 

 of the Medusa, but there is no true analogy between their 

 mutual relations, and those of the vermiform larvae among 

 the Articulata to the perfect insects. The larva developes 

 but a single insect, and, with the exception of its lifeless 

 integument, is wholly transformed into it, but the " Hydra 

 Tuba," after throwing off a whole pile of Medusae from its 

 oral extremity, regenerates its original tentaculated mouth, 

 and returns to the common condition of polype life, till cir- 

 cumstances occur to develope anew a similar reproductive 

 process. )" 



* British, and Foreign Med. Chir. Review. I., 203-212. 

 t Steenstrup on Alternation of Generations, p. 6. British and Foreign 

 Medico Chirurgical Review, as above quoted. 



