K. Fkailson and A. Lek 38!) 



a|>]iarL'iitIy vcry tnistworthy data for difreiuiit spccies. I attribute this, although 

 I liaw not bi'cn ahlc at prescnt to vcrify it, tu preputencij*. In di^aling vvith 

 jiri'potency I tliink it iiiipurlant tu distanguisli uh iiu'tio betweun lliioo kinds : sex- 

 prepoteiici/, iinit preputenci/, antl iiileniiitlent j)rej)uteiici/. By se.i--pi'epüte)ici/ I uikUt- 

 staud Ihat tlio offspring ot' onc ur otiicr sex «r of both scxes are more likii tlio 

 male or the fenialc parent as the ease may bc. Its existeuco is deinonstrated by 

 showing that tlie correlation for onc parent with all the offspring or with one class of 

 offspring is grcater than for the other parent. An exaniination of Table IV. sceins 

 to prove that in man for stature, span and forearni there exists ikj sex-prepotency. 

 ün the otht r band in eyti-eolour in man, thiTe doe.s appear to be a differential sex- 

 prepotency, fatiiiT.s are pre[iotent over mothers for oye-eoionr in sons, and mothors 

 are pri'potent over fathors for tht' same character in ilaiighter.s*. If the ])atc'inai 

 record were trustworthy in tiie ea.se of Basset Honnds — wliii-b 1 am very donbtfnl 

 about — then there would be a large sex-pieputency for all otfspring of the dam 

 over sire in coat-eolour"|'. Froin this sex-prepotency must be di.stinguished an 

 individual prepoteney whieh I terin nnit preputenci/, and which is indepcndent of 

 sex. In unit prepoteney one or other unit in a niating is pre])otent owing to the 

 possession of some physical character, other than a sexual character. This physical 

 character may or may not be that in which the prepoteney shows itself in the 

 offspring. Thns it is conceivable that a dai k-eyed parent of either sex might have 

 a unit prepoteney over a light-eyed parent, not necessarily in eye-colour or in eye- 

 colour «.inly, but possibly in hair-colour, or statnre or mental characters. The unit 

 prepoteney may, however, in no way (Irpcnd upon a simph' observable character like 

 this, but on a subtle combination of j)hysieal factors produciug individual prepoteney 

 in one unit of the pair. To demonstrate the latter form of unit prepoteney will 

 alway.s be a difficnlt problem ; it ccjuld possildj- be attacked by considering the re- 

 duction of variability in the array of offspring of snj)posed unit prepotent matings 

 below the average variability of arrays in which such prepoteney is supposed not to 

 exist. This method would hardly be possible in the case of man where the number 

 of offspring is too small to get the variability of an array free from a very large 

 probable error. It might be effective in the ease of snails, moths, many insects 

 and plants with niimerous oftspring. When unit prepoteney is supposed to be 

 associated with the possession of a definite physical character, it is perfectly 

 possible to attack the problem by the method of association, i.e., investigating the 

 association between the pre.sence (or absence) of this character in a parent and the 

 ratio to total offspring of oft'spring in the array who do (or do not) possess this 

 character, or some other character of the parent in question. If unit jirepotency 

 were absolute we should have the case of "dominauce" as originally propounded 

 by Mendel. 



While we suppose unit prepoteney, — the tendency of one individual out of a 

 pair to be prepotent, — to be chronic, there is another form of prepoteney which we 

 may describe as inter mitteilt. One or other parent may at a partieular mating, or 



* Phih Trum. Vol. 19.5, A, p. 100. See also F. Lutz, niometrika. Vol. ii. p. 234. 

 t li. S. I'roc. Vol. OC), p. 1,57. 



Biometrika ii 50 



