NEW INTERPRETATION OF CNIDARIA 321 



Stand in a causal connection with the longitudinal rows of 

 cilia. 



From this reconstructed form we can deduce without any 

 difficulty both the line which had been pursued in the evolu- 

 tion of the Infusoria with their characteristic mergings of the 

 cytoplasms, the internaUzed sexual phase, and the conjugation; 

 and the line which had been pursued by the Eumetazoa in 

 their evolution with their gametes which become free. 



The Origin of the Middle Body Layer— of the 

 So-Called Mesoderm 



The very large number of known characteristics common to 

 both the Infusoria and the Turbellaria described by v. Gelei 

 has been increased since the publication of his study. In this 

 connection I would like to call attention to the fact that 

 Remane himself, one of the most active opponents of the inter- 

 pretation w^hich suggests a direct relationship between the 

 Infusoria and the Turbellaria and of its consequences, has 

 stated that the numerous similarities that exist in the two 

 groups could not be interpreted as a purely incidental pheno- 

 menon but rather as a proof of a closer relationship; and that 

 they made any further proof i.e. transitional cases, patterns, 

 etc., unnecessary. To this we could add that no facts have 

 become known till now that disprove this close relationship. 

 Furthermore, we must also mention a fact whose value should 

 not be underrated, i.e. that many phenomena can be much 

 more easily understood and explained if viewed from the 

 standpoint of my thesis of the Prociliata as the ancestors of 

 the Acoela, and therefore of the Eumetazoa, than when they 

 are studied on the basis of the old interpretation which believes 

 in a colonial origin of the Metazoa. I would like to mention 

 in this connection the much discussed problem of the origin 

 of the third, or of the middle, body layer, the mesoderm, 

 and the coelom problem^ which is connected with it. 



