PROCESS OF REPRODUCTION IN ORGANISMS. 3! 



where fertilization occurs it does not exist. What possible reason, 

 can there be then for this differentiation, except the reason 

 which exists for the differentiation of any part of the soma? On 

 the other hand, is continued metabolism without some sort of 

 differentiation possible ? 



So long as we do not permit our view of the facts to be obscured 

 or distorted by hypothesis and theory, we cannot, I believe, 

 escape the conclusion that the gametes undergo differentiation 

 because they form as integral physiological parts of differentiating 

 organisms and that they are more highly differentiated than 

 asexual reproductive cells or cell masses because they arise from 

 older or more highly differentiated organisms than these. 



Sexual reproduction is then merely the final term in the repro- 

 ductive series: it is the most highly specialized type of repro- 

 duction. The gamete itself is so highly differentiated and so old 

 that it is incapable of reproduction except with the aid of an 

 external factor. 



V. HEREDITY AND INHERITANCE. 



If the above conclusions are correct it follows that our theories 

 of heredity and inheritance, instead of being based solely or 

 primarily on the phenomena of sexual reproduction, must find 

 their basis for analysis and interpretation of these phenomena in 

 the simpler forms of asexual and experimental reproduction. 

 Sexual reproduction is in many respects the most unfavorable 

 form of reproduction for investigation and analysis of the process 

 of inheritance, for here we find the greatest number of complicat- 

 ing factors, viz., the high differentiation of the gametes, the 

 presence of large masses of non-living material in the egg and the 

 union of different gametes. We can, it is true, subject different 

 gametes to different conditions and observe the result of their 

 union and this method has already given results of great interest 

 and value, but he must be an enthusiast indeed who would main- 

 tain that the complex formulae presented by various recent 

 investigators afford us any real insight into the actual processes 

 of inheritance. Their terms are symbols for something, but for 

 what we do not know and breeding experiments cannot tell us. 

 And to say this is not to detract in any way from the interest 



