392 PROVISIONAL HYPOTHESIS Chap. XXV II 



why does not the amputation or mutilation of a part, especially 

 if effected on both sexes, invariably affect the offspring ? The 

 answer in accordance with our hypothesis probably is that 

 gemmules multiply and are transmitted during a long series 

 of generations — as we see in the reappearance of zebrine 

 stripes on the horse — in the reappearance of muscles and other 

 structures in man which are proper to his lowly organised 

 progenitors, and in many other such cases. Therefore the 

 long-continued inheritance of a part which has been removed 

 during many generations is no real anomaly, for gemmules 

 formerly derived from the part are multiplied and transmitted 

 from generation to generation. 



We have as yet spoken only of the removal of parts, when 

 not followed by morbid action : but when the operation is 

 thus followed, it is certain that the deficiency is sometimes 

 inherited. In a former chapter instances were given, as of a 

 cow, the loss of whose horn was followed by suppuration, and 

 her calves were destitute of a horn on the same side of their 

 heads. But the evidence which admits of no doubt is that 

 given by Brown-Sequard with respect to guinea-pigs, which 

 after their sciatic nerves had been divided, gnawed off their 

 own gangrenous toes, and the toes of their offspring were de- 

 ficient in at least thirteen instances on the corresponding feet. 

 The inheritance of the lost part in several of these cases is all 

 the more remarkable as only One parent was affected ; but we 

 know that a congenital deficiency is often transmitted from 

 one parent alone — for instance, the offspring of hornless cattle 

 of either sex, when crossed with perfect animals, are often 

 hornless. How, then, in accordance with our hypothesis can we 

 account for mutilations being sometimes strongly inherited, if 

 they are followed by diseased action ? The answer probably 

 is that all the gemmules of the mutilated or amputated part 

 are gradually attracted to the diseased surface during the 

 reparative process, and are there destroyed by the morbid 

 action. 



A few words must be added on the complete abortion of 

 organs. When a part becomes diminished by disuse pro- 

 longed during many generations, the principle of economy of 

 growth, together with intercrossing, will tend to reduce it 





