this interchange of concepts is so general that one needs 

 to exercise great care if one would avoid it. 



The theory which postulates the blood-relationship of 

 individuals of the same species may be correct, but it is 

 utterly incapable of proof, and the same is true in a greater 

 degree when there is question of individuals of the same 

 class but of different species. Since a direct proof is im- 

 possible, an attempt was made to construct an indirect 

 proof by a comparison of bodily-organs. But in so doing 

 the Descent theorizers had to relinquish scientific analysis 

 altogether. 



In conclusion Fleischmann states that he does not 

 mean to discard every hypothesis of Descent. He simply 

 gives warning against an over-estimation of the theory. In 

 opposition to those who esteem it as the highest achieve- 

 ment of science, he looks upon it as a necessary evil. Its 

 proper sphere is the laboratory of the man of science, and 

 not the thronging market-place. 



"The Descent hypothesis will meet the same fate (be 

 cast aside), since its incompatibility with facts of ordinary 

 observation is manifesting itself. At the time of its appear- 

 ance in a new form, forty years ago, it exercised a beneficial 

 influence on scientific progress and induced a great number 

 of capable minds to devote themselves to the study of ana- 

 tomical, palaeontological and evolutionary problems. 

 Meanwhile, however, viewed in the light of a constantly in- 

 creasing wealth of actual materials, the hypothesis has be- 

 come antiquated and the labors of its industrious advocates 



130 



