PREVIOUS INTERPRETATIONS OF CNIDARIA 81 



tions to Cnidaria, remained unsolved until a new hypothesis 

 was proposed by me, 39 years ago (Hadzi, 1923 a), according 

 to which Ctenophora had been evolved from planktonic 

 larvae of the polyclad Turbellaria which had been further de- 

 veloped in plankton by way of neoteny. On the basis of this 

 hypothesis we can best explain the much discussed problem of 

 the genetic relationship betw^een Turbellaria and Ctenophora. 

 It has been generally recognized and accepted that there were 

 such close relationship connections, particularly as regards 

 the Polycladida among Turbellaria. In this way we can make a 

 completely satisfactory explanation both of their general forms, 

 as well as of their symmetric conditions, of their internal 

 structures, and of their ontogenies. Th. Krumbach (1928) w^ho 

 made a detailed study of Ctenophora for his Handbuch derZoo- 

 logie (edited Kiikenthal, and later by Krumbach) has given a 

 critical evaluation of all hypotheses which have tried to ex- 

 plain their origin; he has come closest to the best solution when 

 he wrote, "Die Ctenophora stehen den TurbeUarien nahe, ste- 

 hen keiner Bilateriengruppe so nahe wie den TurbeUarien" 

 (p. 978). In the same book E. Bresslau and E. Reisinger (1913) 

 have emphasized how my hypothesis "die eigenartige biradiale 

 Symmetrie der Rippenquallen auf ein Kompromiss zwischen 

 der ererbten bilateralen Symmetrie der Protrochula und der 

 Tendenz zur Radialsymmetrie infolge der planktonischen Le- 

 bensweise zuriickzufiihren sucht." 



L. H. Hyman(I: 693-695) refuses to derive Ctenophora from 

 the Cnidaria, especially out of Hydrozoa (Hydroctena!); she 

 prefers to go further back to the very primitive, i.e. com- 

 pletely indifferent ancestors which she supposes to be common 

 to all the "trachyline-hydrozoan, scyphozoan, and anthozoan 

 Unes." We have already characterized such an attempt to be 

 simply an auxiliary solution. Hyman does not even mention 

 my hypothesis; it is possible that this hypothesis was not known 

 to her even if it is mentioned— though not in the chapter on 

 Ctenophora— in the extensive Handbuch der Zoologie. Hyman, 

 however, finally returns to the problem of Ctenophora in a 



