Vol. XXXIV. April, igi8. No. 4. 



BIOLOGICAL BULLETIN 



CRITICAL NOTES ON THE PRESENT STATUS OF 



THE LENS-PROBLEM. 



E. I. WERBER. 



i. INTRODUCTION. 



The present communication is an attempt to arrive at a com- 

 mon understanding of the nature of the difficulties that stand in 

 the way of the solution of a problem to which for over a quarter 

 of a century have been devoted the best efforts of a number of 

 biological observers. 



One phase of this problem, although at one time rather near 

 solution, has since, owing to apparently unavoidable tech- 

 nical difficulties of the experimental method, become ever more 

 complex. In the following it is my intention to show that this 

 complexity is an artificial one and that it practically disappears 

 on careful sifting of evidence. Owing to this seeming com- 

 plexity, however, an originally correct interpretation has lately 

 been giving way to one that not only is unwarranted, but has 

 already occasioned even some very improbable and fruitless 

 phylogenetic speculations (cf. for instance Becher, '12). 



Anticipating to return to the subject of this communication 

 in a more comprehensive publication in the near future I hope I 

 may be pardoned for incompleteness in considering the pertinent 

 literature at the present time. Only such contributions can here 

 be considered, as from my point of view seem to have the most 

 significant bearing on the problem. 



2. THE ORIGIN OF THE PRIMARY LENS IN ONTOGENY. 



As well known Spemann ('01, '03) was the first to furnish 

 experimental evidence for the correctness of the opinion ad- 

 vanced simultaneously also by Herbst ('01) that the lens of 

 the vertebrate eye is dependent in its origin and differentiation 



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