CHAPTER 2 



THE PREVIOUS INTERPRETATIONS 

 OF CNIDARIA 



We shall now pass on— after this preparatory introduction 

 which has been necessarily rather extensive— to our main 

 problem: what Cnidaria actually are and what is their origin? 

 We shall be better able to understand our new answer to these 

 questions if we first make a critical survey of the interpreta- 

 tions of the nature of Cnidaria w^hich have been proposed till 

 now. It will be sufficient to divide the history of the study of 

 Cnidaria into two parts only, i.e. the first part which begins 

 with Aristotle, and the second part which commences with 

 Leuckart (ca. 1847) and which covers the Darwinian period. 

 From the very beginning the larger Cnidaria, i.e. those that 

 can be observed with the naked eye and therefore more 

 easily accessible (medusae, Siphonophora, Actiniae, corals) 

 have given the impression that they were a kind of organism 

 that resembled the flowering plants. Firmly attached to the 

 ground or moving so slow^ly that this can hardly be noticed, 

 frequently of rich colours, appearing in shrubs, covered with 

 parts that are similar to flowers, and finally stinging like a 

 nettle when touched— all these are properties that are usually 

 attributed only to more highly developed flowering plants. It 

 is therefore not surprising to find acalephs and cnidae men- 

 tioned as early as in Aristotle, and that these same organisms 

 were called sea anemones, sea nettles, phytozoa, etc., by the 

 fishing nations that inhabited the shores of the seas. Later 

 there were various other natural scientists who for a long time 

 saw in these organisms, like Aristotle, something that is at 

 least between an animal and a plant. This is w^hy the name 



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