100 THE EVOLUTION OF THE METAZOA 



kriechenden oder grabenden Formen mit bilateraler Symmet- 

 ric abzuleiten, die spater mit dem Ubergange zur festsitzenden 

 Lebensweise eine radiale Symmetric erworbcn habcn . . . ". 

 However this was as far as Pax could go. In the extensively 

 planned Handbuch der Zoologie where Pax contributed the 

 section on Hexactiniaria the old classification has been preserv- 

 ed: following the example of Kiickenthal wx find the Antho- 

 zoa as usually placed at the end of the system of Cnidaria. 



A similar statement w^as made by the palaeozoologist O. 

 Kuhn (1939) whom I have already mentioned above, according 

 to w^hich all theories must be rejected which "von den Radialien 

 (Coelenterata) die Bilaterien ableiten und in der Ontogenie 

 von Larven den Ubergang von der Radialitat zur Bilateralitat 

 suchen". This statement has had practically no effect whatever 

 (cf. the books by Hyman, Kaestner, etc.) on subsequent 

 authors. 



It is interesting to observe the attitude of neo-zoologists, 

 in their general treatments on Cnidaria, towards the fact of 

 internal bilateral symmetry or bisymmetry in these animals. 

 A. Kaestner (1954) in his recent work on zoology does not 

 even take into consideration this sufficiently important cir- 

 cumstance. At the beginning of his book w^e can only read 

 (1954:9) that "die Coelenterata (9,000 Arten) sind ausserlich 

 gekennzeichnet durch ihren radiaren Bau." In the special 

 part (1954:118) w^e find the brief explanation, "Ihre Anord- 

 nung (sc. of mesenteria) bringt wie der spaltformige Mund 

 einen Zug bilateraler Symmetric in die radiare Anlage der 

 Anthozoa," and, slightly later (1954:121), "die bilaterale 

 Symmetrieachse der Seerose" is briefly mentioned. No explana- 

 tion is given where this disturbance (as it can be justly called) 

 of an otherwise radial symmetry comes from, and of its 

 significance. 



Something else can be found in the manual by Hyman. 

 She does not ignore the actual situation, instead she tries to 

 find some explanation of the internal bilateral symmetry ot 

 Anthozoa— a most unpleasant fact for all the adherents to the 



