ATAVISM. 73 







The tendency to an alternation of generations in 

 the inheritance of disease, which has already been 

 noticed, appears to be analogous in character to the 

 alternations determined by the limitation of defects to 

 one sex, while the other sex alone seems capable of 

 transmitting them. 



In many of the lower animals the alternation of 

 generations is the fixed law of generation. 



In the aphides (plant-lice), for example, nine or 

 ten generations of individuals are produced in succes- 

 sion before those haying sexual organs and capable 

 of producing eggs make their appearance; and this 

 succession of non-sexual generations is uniformly re- 

 peated. 



The phenomena of atavism has been claimed to be 

 but a reversion of the organization to characters be- / 

 longing to an original ancestor or type. 



This, in many instances, appears to be the case ; 

 but, in the alternations that have been observed in the 

 hereditary transmission of disease, and even of normal 

 peculiarities, the theory of reversion is far from satis- 

 factory. 



In the case of Rumpless fowls, as stated by Mr. 

 Hewett, individuals with tail-feathers are of frequent 

 occurrence, and these, as a rule, produce tailless pro- 

 geny. 1 



If, in the case of individuals with tails, there is 

 reversion to the original type, in those without tails, 



cine and Surgery, vol. ii., pp. 221-225, 1813 ; Edinburgh Medical and 

 Surgical Journal, vol. xxxvi., pp. 317-320, 1831 ; and vol. Ixxvii., pp. 

 1-10, 1852. 



1 Tegetmeier's "Poultry-Book," p. 231. 



