CNIDARIA AS THE ONLY COELENTERATA 33 



forms are particularly interesting to a phylogenist. It is 

 only necessary to identify these primitive characteristics 

 which had been typical also for their ancestors, and to inter- 

 pret them correctly. Comparative morphology leads us to find 

 these true homologies. 



In our morphological comparisons we take into considera- 

 tion above all the stages reached by the grown-up animals. 

 This is a point that has been accepted by all morphologists. 

 In Protista we consider the so-called vegetative stage in their 

 cycles of development to correspond to the grown-up stage 

 in metabionts. Secondarily, we have to take into consideration 

 the succeeding stages in the individual, or ontogenetic, develop- 

 ment, starting with the zygote (the fertilized &gg) or even 

 with gametes and with the gametogenesis. The comparison 

 can be made either between various grown-up forms, or 

 between various stages of its development, or, finally, between 

 the grown-up forms and their stages of development. Naturally 

 the latter kind of comparison is to be preferred. 



Here, however, we meet with a problem which has been 

 widely discussed and which has provoked the sharpest contro- 

 versies among the zoologists. This is the question of the rela- 

 tion between ontogenies and phylogenies. The way we under- 

 stand this relationship will be decisive to a large extent for 

 the kind of conclusions we shall reach in individual cases. 

 Here we cannot possibly start to discuss this whole prob- 

 lem; it should suffice to refer to the book by Sir Gavin 

 de Beer, Embryos and Ancestors. Purely as a result of my 

 own research in Cnidaria, and not as a result of the study 

 of the corresponding literature, I came to the conclusion 

 that the now prevailing concept of this relationship which 

 finds its culmination in the well-known "fundamental bioge- 

 netic law" as it has been proposed by Ernst Haeckel, must 

 be basically wrong. The facts that can be established on the 

 basis of a study of the structure as well as of the individual 

 development of Cnidaria disprove decisively the very spirit 

 of this rule (it is better not to speak about laws within the 



