ACALEPH^E. 159 



able to strike its characteristic latteen-sail ; and there also I have seen 

 wrecked a fleet of the "Portuguese men-of-war" (Pht/salia), which 

 had been buojed up by their air-bladders to that iron-bound coast. 



Extremely diversified are both the forms and powers of the free- 

 swimming radiated animals which have been grouped together by the 

 character of their gelatinous tissue and their independent movements. 

 And, in testing the title of this group to be regarded a natural one, 

 the zoologist has first to remark_, that the animals so associated are 

 characterised as they manifest themselves at one stage only of their 

 existence ; and has next to consider the question, what is the relation 

 of this stage to the true or typical form of the species ? 



Zoological ideas of the typical form of a species appear to have been 

 governed by different rules : as, e. g., according to the length of time 

 during which a species may exist under a given form ; or, according 

 to the form mQst commonly presented to observation, and with which 

 we are accordingly best acquainted; or, according to the superior 

 number of the individuals of a species which present a given form, 

 especially where such individuals are produced by gemmation, or 

 otherwise parthenogenetically ; or, lastly, according to the form 

 finally assumed by the individuals developing the ova or spermatozoa. 

 The three former circumstances have plainly influenced the best 

 modern naturalists in the classification of such genera as Campanu- 

 laria and Coryne, which have been placed amongst the Hydrozoa, 

 with the distinctive character of " Progeny medusiform." 



What may be the fate of this progeny, which swarm at certain 

 periods, is not yet quite determined. M. Van Beneden's notion of 

 their metamorphosis into the base of a compound parent, although 

 seemingly natural, is hypothetical. Sars and Steenstrup*s observa- 

 tions of what they believed to be generative organs* or ovaria, de- 

 veloped in the medusiform off"spring of Coryne, more probably point 

 to the right direction of the function and signification of such 

 offspring. The fact that such medusiform progeny do engender ova 

 seems to repose on good evidence, and is important, so far as it goes^ 

 and the processes by which the genetic cycle is completed will be 

 indicated with much probability by the phenomena of that cycle 

 which may be determined in the larger medusiform radiaries. 



If these generate ova and spermatozoa, what then, it may be next 

 asked, do their impregnated ova produce ? If planulas and polypes, 

 then there will be strong ground for concluding the same with respect 

 to the ova of the medusiform progeny of Ccimpanularia and Coryne. 

 That these compound, rooted, hydriform polypes do produce free- 



. * XCIII. p. 29. 



