THE 



BIOLOGICAL PEOBLEM OF TO-DAY 



INTRODUCTION. 



WHAT is development? Does it imply preforma- 

 tion or epigenesis ? This perplexing question of 

 biology has reappeared recently as a problem of the 

 day. Of late years there have been set forth con- 

 tradictory doctrines, each seeking to explain the 

 process by which the fertilised egg-cell, an ap- 

 parently simple beginning, gives rise to the adult 

 organism, which often is exceedingly complicated, 

 and which has the capacity of producing new 

 beginnings like that from which it itself arose. 



The opposing views of to-day were in existence 

 centuries ago, and they are known in the history 

 of science as the theory of preformation or evolu- 

 tion, and the theory of epigenesis. That most 

 of the great biologists of the seventeenth and 

 eighteenth centuries were decided upholders of 

 evolution was the natural result of the con- 

 temporary knowledge of facts. For they knew 

 only the external signs of the process of develop- 



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