REPRODUCTION. 495 



voice, haeniatophilia or tendency to profuse hemorrhage from .slight wounds, 

 gout, epilepsy, and asthma. Psychological inheritances comprise habits of 

 mind, talent, artistic and moral qualities, tastes, traits of character, tempera- 

 ment, ambition, insanity and other mental diseases, and tendencies to crime 

 and to suicide. 



Latent Characters ; Reversion. — Characters that never appear in the parent 

 may yet be transmitted through him from grandparent to child ; such charac- 

 ters are called latent. Among the most striking latent characters are those con- 

 nected with sex. Darwin 1 says : " In every female all the secondary male 

 characters, and in every male all the secondary female characters, apparently 

 exist in a latent state, ready to be evolved under certain conditions." Thus, a 

 girl may inherit female secondary sexual peculiarities of her paternal grand- 

 mother that are latent in her father, or a boy may inherit from his maternal 

 grandfather characteristics that never show in his mother. An excellent 

 example of such transmission, taken from the hcrbivora, is the common one 

 of a bull conveying to his female descendants the good milking qualities of 

 his female ancestors. In the human species hydrocele, necessarily a disease of 

 the male, has been known to be inherited from the maternal grandfather, and 

 hence must have been latent in the mother's organism. That in such cases the 

 character is really potential, though latent in the intermediate ancestor, is 

 rendered probable by such well-known facts as the appearance of female cha- 

 racteristics in castrated males, and of male characteristics in females with dis- 

 eased ovaries or after the end of the normal sexual life. 



Latency may be offered as the explanation of the numerous cases of 

 atavism, or reversion, by which is meant the appearance in an individual of 

 peculiarities that were formerly known only in the grandparents or more 

 remote ancestors, but not in the parents of the individual. This subject is one 

 of the most important in the whole field of heredity. Almost any character 

 may reappear even after many generations. In the human species stronger 

 likeness to grandparents than to parents is a frequent occurrence. The 

 majority of the frequent anomalies of the dissecting-room are regarded as 

 reversions toward the simian ancestors of the human race. The crossing of 

 two strains develops a strong tendency to reversion, and because of this the prin- 

 ciple of atavism must constantly be taken into account by breeders of animals 

 and growers of plants. As an example of reversion after crossing may be 

 mentioned the well-known one, studied by Darwin, of the frequent appear- 

 ance of marked stripes upon the legs of the mule, the mule being a hybrid 

 from the horse and the ass, both of which are comparatively unstriped but 

 are undoubtedly descended from a striped zebra-like ancestor. Here the 

 capacity of developing stripes is regarded as latent in both the horse and the 

 ass, but as made evident in the mule by the mysterious influence of crossing, 

 Darwin thinks likewise that the customary degraded state of half-castes mav 

 be due to reversion to a primitive savage condition which, usually latent in 



1 Charles Darwin : The Variation of Animals <uul Plants under Domestication, 1892, vol. ii., 

 •2d ed. 



