SIPHONOPHORA. 137 



nemal gastral pouches) ; without otoporpae. Solmissus H. ; Solmundus H. ; 

 Solmundclla H. ; Solmoncta H. ; Solmaris H. 



Limnocnida,* a fresh-water Medusa from Lake Tanganyika, is probably allied 

 here. 



Order 7. SIPHONOPHORA. f 



Free-sic im m ing polymorphic colonies of Hydromedusae prod wed l>y 

 lud/Ung from an original, probably medusoid, individual. Gonads in 

 yonophores which, as a rule, are not set free. 



The colonies of the Siphonophora are characterised by the extreme 

 specialization of the individuals composing them. So great indeed 

 is this specialization that some zoologists (Eschscholtz, Huxley, 

 Metscknikoff) have held the view that their component parts are 

 really organs of a single niedusoid individual, which is distinguished 

 from an ordinary medusa by the fact that its various parts rnanu- 

 brium, tentacles, umbrella have multiplied independently of one 

 another, and have become differentiated and in part dislocated from 

 their primitive positions ; in short, that a siphonophore, in possessing 

 in a marked degree the power of vegetative increase of its parts, 

 resembles a plant more than an animal. 



This multiplication of the parts of an organism, often independently of one 

 another, is not however by any means exclusively a vegetable characteristic. 

 It must have happened largely in the animal kingdom, and have been a potent 

 factor in determining the forms of animal life. 



Another view, and the one more generally held, is that they are 

 free-swimming polymorphic colonies of highly specialized polyps, 

 with the power of producing medusae (Vogt, Leuckart, Gegenbaur, 

 Glaus, Chun). 



According to it, all the parts of a siphonophore are either modified 

 polyps or medusae, and the primitive zooid of the colony is of the 

 polyp type. Just as the first theory errs too much in denying the 

 colonial origin of our group, so the second theory probably goes too 

 far in affirming it. It is probable that the truth lies between the 

 two views. We hold, with Haeckel and Balfour, that the colonial 

 theory is the true one, but that the primitive zooid of the colony 

 was probably a medusa which has produced other medusae by 

 budding, and that the parts of these medusae possess the power 

 of becoming discrete and removed from the bud to which they 

 belong, and of becoming in some cases secondarily multiplied. So 



* R. T. Giinther, Quart. J. Mic. Sci., vol. 36, p. 284. 



t E. Haeckel, "Report on the Siphonophorae," Challenger Eeports, vol. 28, 

 1888. C. Chun, "Die Canarischen Siphonophoren," I. and II., Abhandlungen d. 

 Senckenbcrgischen naturf. Gesellsch. 1891-2. 



