Organism of the Siphonophora. 191 



of assertions are posited as axioms and adopted as established 

 propositions in the schematization of the new Medusome- 

 theorj. 



How does Haeckel prove to us that the primary Medusiforra 

 Siphonophoran larva is to be interpreted paling enetically , 

 and demonstrate the truth of the assumption of an extensive 

 multiplication and dislocation of the individual organs of the 

 Medusa '? And to what new factual conditions does he appeal 

 when, as arbitrator in this main question, he rejects as erro- 

 neous the opposite view, which denies a far-reaching secondary 

 multiplication and dislocation of these organs, and regards 

 the primary Medusiform larva as a ca3nogenetic form ? Or is 

 it more than an axiom to start from a bilateral Medusa as the 

 primary larva or " siphonula," which, distinguished by a 

 ventral umbrellar fissure and the possession of a single mar- 

 ginal filament, has originated from a primaeval bilateral stem- 

 ibrm of the Anthomedusan group, to be christened " Proto- 

 meda " ? How long, in Hackel's system, has the l)ilateral 

 symmetry, which, according to his Gastrtea-theory, is pro- 

 duced as a consequence of a creeping mode of life, been thus 

 a primitive character of the Medusa, the ontogenetic develop- 

 ment of which on the Hydroid-stock would indicate a regular 

 radiate fundamental form ? 



By such a dogmatic assertion, at variance with all obser- 

 vation, we certainly escape answering the question * in wliat 

 manner the stomachal tube and tentacles have passed from 

 the centre and the umbrellar margin to the outside of the 

 Medusan umbrella, and what advantage this deviation from 

 the radiate fundamental form could have had for the main- 

 tenance of the organism, but without considering that in tliis 

 way the knot has been cut and not loosened. 



It is the same with the second axiom, which gives Haeckel's 

 Medusa-theory its special character, namely the assumption of 

 a second primitive stem-form of octoradial structure of the 

 Trachymedusan group, called the " Archimeda," in order to 

 derive therefrom a second Medusiform larva, the "Diseonula," 

 which, in possession of a marginal circlet of tentacles, has 

 produced the individuals of the stock by gemmation from tlie 

 subumbrella, and formed the starting-point for the develop- 

 ment of the Piscoidea {Porpita^ Velella), rechristened Disco- 

 nanthai. By this hypothesis and the supposition involved in 

 it of a diphyletic origin of the Siphonophora, Haeckel's theory 

 certainly beomes a neto variety of the Medusa-theory, but at 

 the same time it loses probability in the same degree that the 



* See Glaus, " Ueber das Verhiiltniss von Monophjes zur den Diphyiden 

 &c.," in Arbeiteu des Zool. Instituts &c. (Vienna, 1883), p. 9. 



