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duced before the conclusion of the conjugation of the gametes 

 derived from the parent generation, but is the product of the 

 completed conjugation of the gametes derived from the grand- 

 parental generation. 



Though we may for some purposes make a contrast between 

 the two generations, describing one as conjugate and the other as 

 perjugate, this should not cause us to forget that all organisms 

 of the higher groups are conjugate organisms. This is in fun- 

 damental contrast with the exjugate organisms of the lower 

 groups, which are built up, not during conjugation, but in the 

 intervals after, or between, conjugations. 



This system of reproduction of the higher plants and animals, 

 which enables them to build up new organisms while conjuga- 

 tion continues, and before it is completed, is responsible for the 

 ability of the higher groups to form sterile hybrids, that is, 

 hybrids between groups which are so diverse that their gametes 

 are unable to effect a complete conjugation, so that no perjugate 

 generation is produced. Such conjugate hybrids are an impos- 

 sibility, of course, among the lower groups where conjugation 

 has to be completed before cell-divisions begin. 



Thus Mendelism is not the onl}?^ phenomenon which results 

 from the fact that higher organisms are built up before the con- 

 jugation of the parent gametes is completed. Conjugate hybrids 

 prove that the conjugate relation is different and less exacting 

 than the perjugate relation, and may thus help to reconcile us 

 to the fact that differences between the two generations are 

 inherent in the method of reproduction and not necessarily indi- 

 cative of general principles of inheritance. Indeed, it is claimed 

 by some Mendelians, such as Castle and Allen, that dominance, 

 the relation sustained by the gametes in the conjugate genera- 

 tion, has nothing to do with what they consider Mendelism 

 proper, the '* principle of gametic purity."^ 



'Castle, W. E., and Allen, Glover M.,1903. Mendel's Law and the Heredity 

 of Albinism. Mark Anniversary Volume, pp. 3S3. Henry Holt and Co., N. Y. 



" The principle illustrated by these examples is, as pointed out by Bateson, 

 the most fundamental and farreaching of the Mendelian ideas. It is known as 

 the " law of segregation," or " splitting" of the parental characters at gamete- 

 formation, or as the " principle of gametic purity." Dominance is purely a 

 secondary matter ; it may or may not occur along with segregation, though the 



