Organism of the Siphonophora. 193 



genetic development of the Medusa by Hydroid-stocks entirely 

 out of consideration. That is the central and at the same 

 time the weakest point of the theory, which at once brings 

 the opposition to the Hydroid-theory into prominence. This 

 commences with the older and original metagenetic develop- 

 ment of the stem-form, and refers the resemblance to a bilate- 

 rally constructed Medusa which makes its appearance so early 

 in the young Siphonophoran larva, only to external analogies 

 secondarily produced. In this the Siphonophoran larva does 

 not appear as the repetition of a primitive, hypogenetically 

 reproducing, bilateral Oceanid with dislocated stomachal tube 

 and marginal filaments, whicli by continued gemmation of 

 new Medusse and parts of MedusiB produces tlie polymorphic 

 stock, but a free-swimming developmental stage of the 

 Hydroid-stock of an Oceanid reproducing metagenetically^ 

 furnished the starting-point for the production of the Siphono- 

 phora, and in fact the prevention of fixation was the cause of 

 the first change, the occasion of a series of transformations 

 which then also affected the sexual Medusse budding forth 

 from the stock. Of course, in the absence of any data fur- 

 nished by transitional stages and intermediate forms, it must 

 be left to fancy to finish the picture of tlie changes through 

 which in the phylogenetic process the original form resembling 

 a larval Hydractinia or Podocoryne could have transformed 

 itself into a Siphonophoran. It is only in this light that the 

 attempt made in my little paper is to be judged, as a repre- 

 sentation which, when compared with the picture of the 

 budding Medusa, has at least an equal justification. The 

 reconciliation between the Medusa- and Hydroid-theories 

 which I attempted in this statement therefore depended upon 

 the proof that, while for the former the conception of the 

 Siphonophore as a polymorphic stock appears by no means 

 excluded, the second theory also presupposes the presence in 

 the stem-form of a Hydroid Medusa. I could approve of the 

 Medusa-theory in so far as it starts from the Hydromedusa, 

 but could not concede to it that this is to be found repeated 

 even in the primary larva, and that the latter was to be palin- 

 genetically interpreted. On the other hand, I defended the 

 Hyflroid-theory, in tlie conception of the polymorphic stock 

 in which 1 found no contradiction to the former with reference 

 to the starting-point of the iSiphonophora, which is to be 

 sought not in the mature Hydroid-stock, but in the free- 

 swimming larval stock. The supposed stem-form was not a 

 symmetrical Medusa with dislocated organs and hypogenetic 

 development, but a metagenetically developing, normally con- 

 structed .Medusa, in the swimming larval stocks of which the 



