ALTERNATION OF GENERATIONS. 121 



to consider tlie polype form as a rudimentary phase, com- 

 parable to that occurring among the Trematoda, and to re - 

 gard as typical the Medusa form, which is an animal of 

 much more conspicuous appearance, of apparently higher 

 organization, endued with the power of . locomotion, and 

 havinor true sexual ors^ans in distinct individuals. Such, 

 indeed, is the view taken by Steenstrup and several other 

 authors, even by those who occasionally speak of the medu- 

 soid progeny of the Hydraform polypes as mere detached 

 generative organs. Thus Prof. Owen observes — " The 

 nutritive gemmiparous polypiform individuals in all the 

 compound Radiaries would seem, rather than the oviparous 

 medusiform ones, to manifest the typical form of the 

 species. . . . Superadd, however, distinct nutritive 

 and circulating organs to the free-moving ovigerous indi- 

 vidual from the rooted polype, and prolong its existence, 

 and it would then cease to have the ancillary character of a 

 nurse to the ova of the fixed individuals, and would assume 

 that of the perfected form of the species ; and such in fact 

 is the case with the larger gelatinous Eadiaries called 

 Medusse." * 



Now, in so far as perfection means the possession of a 

 more conspicuous organization, it is not of course to be 

 denied that the Medusa is in advance of the polype ; but 

 as regards the selection of the phase to be taken as the 

 typical form of the species, I do not see how we can avoid 

 these conclusions — 



1. That the Medusoids derived from the compound 

 polypes (Sertularida and others) — formerly ranked as a dis- 

 tinct order under the name of Gymnophthalmatous (or bare- 

 eyed) Medusae — are really homologues of the parts of re- 

 production, inasmuch as they pass by a continuous grada- 

 tion into generative organs of the simplest kind. 



* PartlienogenesiSj p. 12. 



Q 



