PREVIOUS INTERPRETATIONS OF CNIDARIA 99 



We can observe in Cnidaria, as this has already been the 

 case with Ctenophora, that they also adhere to the rule accor- 

 ding to which the arrangement of the internal organs or parts 

 towards symmetrical conditions, is much more definite than 

 that of the peripheral organs. The external form soon becomes 

 changed to a radially symmetrical construction due to the 

 sessile w^ay of life or posture when the animal is firmly attached 

 at one end of its body; this has taken place in such a way 

 that the body which was initially more or less flattened, took 

 on a cylindric form. The earlier ventral and dorsal sides which 

 had previously slightly differed from each other have thus 

 obtained an identical form; the tentacles which in all proba- 

 bility had been earlier arranged in the form of a bow or of 

 a horse-shoe and whose number has been increased by way 

 of polymerization, have now developed into regular circlets. 

 Yet at the same time we find that in the digestive organs of 

 anthopolyps— and this is actually the septal apparatus— the 

 remains of an earlier bilateral symmetry have been preserved. 

 In ontogeny such traces have also been preserved in the pro- 

 cess of the formation of tentacles. Some insignificant remains 

 of this old bilateral symmetry can also be found in the young 

 scyphopolyps (the so-called scyphistomae). Any trace of a 

 former bilateral symmetry, however, is completely lost in 

 the adult Scyphozoa and particularly in the Hydrozoa. 



There have been some neo-2oologists who did not take 

 easily to the fact of an internal bilateral symmetry observed 

 in Anthozoa. As early as 1879 it has been proposed by Haake 

 (according to Pax 1954, 288), that the primitive form of 

 "Zoophyta" must have been bilaterally symmetric and that 

 it has later become radially symmetrical because of their later 

 transition to a sessile way of life. Professor Dr. Ferdinand 

 Pax, an expert on the Anthozoa, pointed to the fact, in 1914, 

 "dass viele der primitivsten Aktinien, die noch einer Fusscheibe 

 entbehren, durch eine bilaterale Symmetric ausgezeichnet 

 sind" (Pax, 1954:2889). On the basis of this Pax concluded, 

 "Man konnte daher geneigt sein, die Aktinien von fusslosen. 



