PREVIOUS INTERPRETATIONS OF CNIDARIA 103 



called a Bilaterogastraea (Fig. 55). He placed it between the 

 blastea which had lived in plankton and those Metazoa that 

 actually exist. He believed that this was an animal which had 

 crept over the sea bottom, and in this it differed from the classi- 

 cal planktonic gastraea. Jagersten's theory of a bilaterogastraea 

 is essentially a variant of the old theory of Enterocoela which 

 had been proposed by Leuckart and Sedgwick. The only diffe- 

 rence is that here the Anlagen of the three pairs of the future 

 coelom cavities are connected with a somewhat higher stage 

 of development than the old gastraea had been. This is a typi- 

 cal suitcase theory (Koffertheorie) which is so general and all- 

 embracing that with only a small modification it will explain 

 anything! I have examined the opinions proposed by Jagers- 

 ten (Hadzi 1955), and I have rejected them because I have found 

 this interpretation improbable and unacceptable. Jagersten's 

 ideas will necessarily have the same fate as the ideas of the 

 blastea and of the gastraea which had been proposed by Haeckel. 

 These ideas have finally had to be abandoned and there is no 

 modernization which could help them. In Jagersten's con- 

 cept, there are individual points only that are correct, e.g. his 

 opinion that the Cnidaria had been originally bilaterally sym- 

 metric animals, that the Anthozoa are the oldest form of Cni- 

 daria, that primarily they had no medusoid form, and, finally, 

 that cnidae had been progressively developed within aU the 

 group of Cnidaria. All this was already published by me years 

 ago. Later we will return to Jagersten's proposal to derive 

 Metazoa from the Protista. 



Why Is There No Medusoid Form 

 in Anthozoa? 



So far scholars have carelessly bypassed the fact that there is 

 no medusoid generation in Anthozoa. This has simply been 

 taken for granted, an attitude that is partly understandable on 

 behaLfof the adherents to the thesis that the Hydrozoa are the 



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