94 THE EVOLUTION OF THE META20A 



concept proposed by Moser— according to which the form of 

 the ancestors of Cnidaria is recapitulated in the siphonula, or 

 in the larva of Siphonophora— is unacceptable and wrong; 

 and the consequences of this supposition are even more so. 

 An individual can never be developed out of an organ, 

 neither can a polyp be evolved out of a medusa. According 

 to this hypothesis proposed by Moser, the Hydromedusae 

 had been developed four times independently from each other, 

 both in plankton as well as in the benthos. It can be truly 

 said that, fortunately enough, Moser has never been followed 

 by anybody else in this interpretation she had proposed. 

 It must be regretted that such an obviously improbable con- 

 struction could have found admittance into a representative 

 manual on zoology. The construction itself has a purely 

 historical interest now as an entirely erroneous attempt. 



Finally we must mention here also the case of Halammohydra, 

 an aberrant Narcomedusa (see Hadzi, 1959 b), Halammohydra 

 is actually not the only Hydromedusa that has readopted 

 a benthonic way of life, yet in their evolution they have deve- 

 loped farthest away from the typical medusa form because 

 they have become adapted to a Ufe in sand on the sea bottom 

 (Fig. 18). One could expect that they would evolve into a 

 polyp form. Yet here the validity of Dollo's rule of irrever- 

 sibility has again been proved. Though Halammohydra has 

 undergone a very considerable change, this change, has not 

 been so intensive (fortunately enough for zoologists!) that 

 their nature as Narcomedusae could not be clearly recognized. 

 The supposed polypoid characteristics which have been 

 thought to have been identified by A. Remane, the discoverer 

 of this aberrant form, and by other scholars, are in reality 

 the excessively changed medusoid properties only, the general 

 polypoid shape is due to a strong reduction of the umbrella 

 and to a considerable lengthening of the manubium. It is 

 interesting to notice that a general ciUation of its skin has 

 secondarily reappeared in this medusa, a case which has been 

 explained by A. Remane as an indication of a neoteny. Thus 



