118 THE NATURE AND VARIETIES OF 



Now, while this case agrees with that of the Trematoda, 

 in the first of the three characters before given that of a 

 derivation of sexual and oviparous zooids (the medusoids) 

 from others which are sexless and gemmiparous (the polypes, 

 or their common stem, or its capsular developments) I 

 think it may be clearly shown to differ in the other two ; 

 that is to say, in the zooids which represent the typical 

 form being here the earlier or gemmiparous set, not the 

 later or oviparous ; and in the process of gemmation being 

 ancillary to the act of sexual reproduction, instead of re- 

 presenting a step in the development of the typical form 

 belonging to the Gamomorphic, instead of to the Proto- 

 morphic stage. 



Certainly it is the polypiferous phase which in the great 

 majority of the species impresses us as the representative of 

 the typical form, for in the Coryniform and Sertularian 

 zoophytes, as well as in the Calycophoridae and Physopho- 

 ridse, the individual polypes, though small, are sometimes 

 not so minute as the resulting medusoids ; while the zoo- 

 phytic growths, which are developed by their repeated pul- 

 lulation, are clearly the most conspicuous phase in the life- 

 history of the species, and, in the two orders last mentioned, 

 have often such individuality of character about them, that 

 they suggest the idea not so much of a colony of aggregated 

 zooids, as of a body composed of various organs, like that 

 of one of the higher animals.* 



And as in these cases the polype phase is the most con- 

 spicuous, so is it always the most permanent condition, for, 

 after throwing off a swarm of medusoids, it goes on in as 

 vigorous a state as before, and at intervals, varying with the 

 species or with accidental circumstances, may give origin to 



* This is especially the case in such forms as Physalia, Velella, and 

 Porpita. 



