v AIMS OF EXPERIMENTAL EVOLUTION 255 



What is heredity ? how does it operate ? what is 

 transmitted ? We hardly know anything on the 

 matter ; we all have read a number of anecdotes of 

 more or less unscientific character, and remain in the 

 dark. Weismann's solid and heavy essays are cer- 

 tainly valuable, but facts must be added to reasonings, 

 and the facts we need are mainly experimental. The 

 whole problem requires a thorough investigation, al- 

 though many facts are already ascertained, a great 

 deal remains to be done to explain heredity, and 

 to ascertain its limits and power. One important 

 question is that of the heredity of Abnormalities and 

 Mutilations. Many abnormalities, when not opposed 

 to the continuation of life, are hereditary. 1 A good 

 instance is provided in the case of the cats, mentioned 

 by E. B. Poulton (^^^,1883-6), and in the case of the 

 Fodli tribe, in Arabia, where all the individuals, since 

 very ancient times, have been born with twenty-four 

 digits instead of twenty, and where they all marry 

 within the tribe. 2 Many diseases are hereditary, under 



1 Paul Bert must be included among those who have somewhat 

 investigated the subject, after Philipeaux, Bronn, and many others. 

 He observed that if the eyes of young, newly-born rats are re- 

 moved, death always ensues when the experiment attains the fourth 

 generation, doubtless, says he, through some impairment of the optic 

 lobes. Cf. his Essais cf Experience sur la Transmission hereditaire de 

 certaines Lesions chirurgicales ; Relations trophiqnes entre les Yetix tt 

 les Lobes optiques. Comptes Rendus Soc. de Biologic, 1870. 



2 Aira, Bull. Soc. Anthropelogie, 1886, 



