VIII 



Comparison of the Genetic Phenomena in the Protozoa 

 with Those in Higher Organisms. General View of Develop- 

 ment, Mating and Evolution. 



HOW far does the condition of affairs which we have set 

 forth for the lower organisms hold for the higher 

 ones ? 



As we have remarked at various points in our earlier 

 lectures, many, perhaps most, of the general relations are 

 similar in the lower and higher organisms. But there are 

 certain points in regard to which questions may be raised; 

 particularly as to the origin of new hereditary characters. 

 The points needing examination are mainly (1) as to the 

 effect of the environment in causing inherited changes, and 

 (2) as to the nature and extent of the changes in hereditary 

 characters that arise in nature; with the relation of these 

 to the process of evolution. 



We have dealt in our fourth lecture with alteration of the 

 hereditary constitution of lower organisms by external con- 

 ditions. In the higher, more complex organisms the under- 

 lying conditions as to this are somewhat different from those 

 found in organisms composed of but a single cell; though 

 perhaps not so completely diverse as is sometimes conceived. 

 But in the higher organisms there is a great mass of cells, 

 the body, which finally disintegrates completely, without 

 propagating itself by division ; the body of the next genera- 

 tion is formed, not from the body of the preceding genera- 



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