394 THE EVOLUTION OF THE METAZOA 



relationship between the Mollusca and the Annelida have 

 referred above all to the similarity that can be observed in 

 their planktonic larvae of the trochophore type and to the 

 spiral cleavage. We have already shown that neither an external 

 similarity w^hich can be found in larval forms nor a spiral 

 cleavage can be used as firm proofs of a closer relationship 

 between two animal groups. The situation is perfectly clear 

 as regards the coelom conditions and the segmentation ; a 

 polymerization frequently takes place in the primitive Mollusca 

 and in Neopilina (which is not a primitive mollusc but rather 

 a primitive gastropod); this polymerization disappears in the 

 higher subtypes and it is only partly preserved in the Cephal- 

 opoda (Tetrabranchiata). This, however, should not be inter- 

 preted as a remnant of a genuine segmentation but rather as 

 a minimal polymerization. Zoologists have endeavoured to 

 find by all means at least in the ontogenies a recapitulation 

 of a formation of genuine metameres (of the perigastrocoele); 

 they have even maintained that they have found something 

 of this kind. Yet they actually saw something that does not 

 really exist because that was w^hat they wished to see. We can 

 best see how^ much we are justified in classifying the Mollusca 

 among the Ameria if we compare the lower and the lowest 

 Mollusca— which differ only slightly from the probable initial 

 form w^hich stood close to the Turbellaria— with the other 

 Ameria, and if we do not include first into such a comparison 

 the highest Mollusca, the Cephalopoda. 



H. Lemche went too far in his display of his scientific 

 imagination (which can be quite useful if it is used within 

 proper limits) when he tried to exploit the discovery of 

 Neopilina. My opinion is shared by numerous other zoologists 

 (cf. the discussion by C. Bottger and by others at the XVIth 

 International Congress of Zoologists). There is no factual justifica- 

 tion for a derivation of the primitive Arthropoda from the 

 Mollusca, and above all of the articulated extremities from 

 the ctenidia. In the primitive Mollusca we can find a 

 somewhat stronger trend to the polymerization, just as is the 



