possessed a multiple origin, the problem of the extinction 

 of the saurians would, according to Steinmann solve itself. 

 One would not need to consider the number of extinct forms 

 as large as is now done. However, he does not enter upon 

 any closer consideration of this question. But he points 

 out, for instance, that to-day the shells of mollusks (snails 

 and conchylia) are regarded as structures that were acquired 

 only in the course. of time for the sake of protection, the 

 disappearance of which, therefore, impHed a disadvantage 

 for the respective organisms. This transition would be 

 something extraordinary — "but if on the contrary, one re- 

 gards the shells as the necessary products of a special kind 

 of assimilation and of the immoveableness of certain parts 

 of the body, the gradual disappearance might well be con- 

 sidered a process which may take place in various animal- 

 groups with a certain regularity in the course of the phy- 

 letic development." The snails devoid of shells, for in- 

 stance, may be derived with certainty from those possessed 

 of shells ; this process has very probably also taken place in 

 different genetic lines. 



This view is well worth consideration; it stands in 

 sharp opposition, in fundamental principles, to the Dar- 

 winian explanation. This calls for special emphasis here. 

 How should one explain the origin of uncrusted mollusks 

 from crusted ones through the struggle for existence, since 

 in such a contest the latter must have had far greater pros- 

 pect of survival than the former? 



This view together with the principle of multiple ori- 

 gin opens up, according to Steinmann, "the prospect of 



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