MENDELISM AND OTHER .METHODS OF DESCENT 213 



tion of polarity of expression to an ancestral character which 

 has remained latent for numerous generations. In conjugate 

 reversion the change of polarity comes about through the bring- 

 ing of the gametes together in fertilization. In perjugate rever- 

 sion the change of polarity probably occurs at mitapsis, when 

 the new gametes are formed. Perjugate reversion may also be 

 described as mitaptic reversion or as gamete reversion, when it 

 is desired to emphasize these contrasts. But from the stand- 

 point of analogy with Mendelism perjugate reversion seems the 

 better term, since it indicates more definitely the fact that the 

 reappearance of the previously latent ancestral character does 

 not become evident in the conjugate generation, but in the 

 perjugate. 



A curiously complex instance of reversion in later perjugate 

 generations has been reported recently in pigs. Two three- 

 quarters Berkskire and Poland China sows, when bred to a simi- 

 larly crossed male produced litters of pigs each of which showed, 

 while young, seven longitudinal stripes like wild pigs. The 

 parents had retained the black color and white points of the 

 parent breeds. The mating of a pair of the pigs which had 

 been striped when young yielded a diverse litter, some with the 

 ancestral stripes, some with solid sandy black, the usual colora- 

 tion of the Berkshire breed of sixty years ago, and some with 

 black and white spots like the Poland Chinas of thirty years 

 ago.' 



Prepotent Polarity. — This is a form of polarized descent in 

 which the divergent character of one parent is expressed in more 

 than three-quarters of the perjugates, showing that more than 

 half of the prejugate gametes tend to express the character of 

 the one parent. 



An instance which may be interpreted as polar prepotency 

 is described by Professor De Vries. All thfe seeds of a plant 

 which had shown only a few ligulate disk-flowers produced 

 plants with completely double flowers. The expression of the 

 double variation may have been restricted in the first genera- 

 tion by the non-mutated gamete, but the new character appears 



^Simpson, Q^. I. and J. P., 1907. Reversion Induced by Cross-Breeding. 

 Science, N. S., 25: 427. 



