OF THE I-IYDROMEDUSiE. 375 



ent from the adult, and that, during- its youth, it undergoes a complicated metamor- 

 phosis. 



It is generally staled in the monographs as well as in the text books that although the 

 young medusa is unlike the adult, there are no true larval stages, since the egg gives rise 

 directly to a medusa, which becomes metamorphosed, through a series of changes, into 

 the adult. 



This is, as I shall show, an erroneous interpretation of the facts, for the published ac- 

 counts, when rightly interpreted, show that the larva actually passes, like (.(her hvdrome- 

 dusse, through a planula stage and a hydra stage, although naturalists have been misled 

 by th-3 fact that the hydra-larva is locomotive, and as it does not mull iply asexually the fact 

 that it is a time hydra has been entirely overlooked; and, so far as I am aware, not a sin- 

 gle naturalist has noticed the existence of a hydra stage. 



M >st writers in fact have been so firmly impressed with the belief that medusa? have 

 originated from sessile hydroid communities, that they have not only overlooked this 

 stage in the development of the Geryonkhe, but they have expressly stated that it has 

 disappeared. Thus Balfour states (65, p. 153) that The Trachomedusa? are * * * "prob- 

 ably derived from gonophores in which the trophosome disappeared from the develop- 

 mental cycle," and Haeekel says (31) of the development of the Trachomedusae: "This 

 form of ontogenesis is to be regarded as a secondary or cenogenetic process, which has 

 originated from the primitive metagenetic mode of development through the loss of the 

 polyp generation." See alsoLendenfeld ( 10, p. 448). 



So far as I am aware, Bohm is the only writer who has recognized the possibility of any 

 other explanation, and he dismisses the subject very briefly and makes no reference to 

 the Trachomedusa?, although he does not believe that alternation of generations is prim- 

 itive, and suggests (9, p.. 158) that "Lucernaria, the Ctenophora, the free Siphonophora 

 {and possibly some of tin m< dusce without a polyp-generation f) may be the direct descend- 

 ants of a free ancestral form without the intervention of a sessile stage." 



The total absence of anything like alternation of generations gives especial importance 

 to the occurrence of a hydra stage in the life-history of the Geryonida?, and furnishes a 

 key for the interpretation of the more complicated life-histories of other Hydromedusae, 

 proving, as I think, the correctness of the view so briefly hinted by Bohm ; and I therefore 

 give in PI. 41 figures of various stages in the life of Liriope scutigera. The develop- 

 ment of this species has never been described, although we have in Fofs paper on the 

 embryology of Cferyonia fungiformis (22) and those by Metschnikoff (51, 52) on Gery- 

 onia fungiformis, Geryonia hastata and Liriope eurybia, a very complete history of 

 closely allied species. 



Ray Lankester has stated in a recent paper that Fol, in his well known and valuable 

 monograph "has completely failed to give even an approximately correct account of 

 them alter" and that Metschnikoff's description is "erroneous" (45). As my own ob- 

 servations on our American Liriope agree in every essential particular with the accounts 

 by Fol and Metschnikoff it seems proper to give, in detail, my verification of the excel- 

 lent researches which are thus sweepingly condemned. 



I have been able to add a few points, such as the origin of the mouth, and of the radial 



