PROBLEMS OF MODERN SCIENCE 



just as the lens develops from the superficial layer 

 of the skin opposite to the vesicle in the normal eye. 

 This experiment demonstrates in a very beautiful 

 manner the correlation which exists between the 

 development of different organs of the body. 

 Evidently the appearance of the lens depends 

 upon the presence of the optic vesicle, and it is 

 probably initiated by a stimulus exerted by some 

 chemical substance secreted by the latter. In this 

 field again we find abundant material for the logo- 

 machies of mechanists and vitalists. 



The student of Genetics, which may be defined 

 for our purposes as the experimental study of 

 heredity, concerns himself with the unravelling of 

 the mysterious connection which exists between 

 parent and offspring. Since the opening of the 

 present century this department of our science 

 has been dominated almost exclusively by the 

 Mendelian school, who are developing in every 

 direction, and in the most thorough manner, the 

 line of investigation initiated by the Abb Mendel 

 himself half a century earlier. 



The knowledge that new organic types, differ- 

 ing in one or more respects from any of their 

 ancestors, may arise from the crossing of different 

 varieties, and may, in certain cases, propagate their 

 own peculiarities, has not only been very fruitful 

 in results of practical importance, but has rendered 

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