PRESENT PROr.LEMS IX EVOLUTIOX AXl) HEREDITY. 369 



specific bill (liMciciit iiulividual Iciidciicics. K'libl. an cmiiicnr oin- 

 bryologist, shares this \ic\\ . and it is suitpoitcd by BoNcii iipou the 

 observation that in each (li\ ision tlic paternal and nniternal elements 

 are kept distinct, and in .iscdris. lor cxani]>le. two of the cluoinasomes 

 of each divisittn Hjinre are paternal and two are maternal. 



In favoi- of tills hypoth(\sis Ave may jtlace the following,' facts: 1st, 

 that there are an even nnmber of chroinasonie rods in all cells; 2d, that 

 the number is constant throughout all tlie snbse<iuent changes in tlie 

 tissues; 3d. that tlie iunnl)er is fixed for each si)ecies or variety; 4th, 

 that the number is the same in each s<'.\. 



Against this replacement hypothesis we must consider the extreme 

 complexity of the division process, and tlie hmg-resting, or thread 

 stage, in Miiich the chromatin lies in a confused coil. Further. Hert- 

 ■\vig argues that if the elements are distinct we should find some evidence 

 that the mateiiial or ]»aternal part is a troi)hied or replaced, or excluded 

 from the nucleus, fctr botli parts can not share alike in the control of 

 the ceil. These are llertwig's grouuds for supporting the ''verschmel- 

 sungstheorie."' or fusion theory, also advocated by Waldeyer, to the 

 effect that l)y the complete union of the maternal and paternal sub- 

 stance a new product is formed; in this fusion the law of pre-j)<>tency 

 may come into play", causing one or other of the parental tendencies to 

 predominate, or there may be an even re-distribution, whereby, as ex- 

 pressed by llensen, ''the hereditary substance of the son is not that 

 of the lather plus that of the mother, but is his own, with a new heredi- 

 tary form resulting from the combination."' 



While suspending Judgment between these two views as ro the sej)- 

 aration or fusion of the chromatin, wo may appeal to the external 

 l^henomena of heredity for light u]>on the probabilities in the <piestion 

 First, 1 refer to the very decided opinion of Francis Galton in regard to 

 ])articulafe inheritance; he is so impressed with the fact that we are 

 made uj) bit by bit of separate structures derived from different ances- 

 tors that he has even suggested that the skin of the mulatto may 

 I'epresent not a fusion of wliite and l)lack, ])iit an excessively fine 

 mosaic in wJiich the ccdors are so distributed as togiv(^ the a]»])earance 

 of blending. We do sometimes observe ]>atches of color as evidence 

 of uneven distribution, AsGaltou distinguishes two ty])es of structures 

 with referenee to inheritance, viz, those which blend and those which 

 do not blend, we might ccnrelale these types Avith ]U"e jiotency, replace- 

 ment, and fusion. Wlieic characteristics do not blend, as in eye-color, 

 it is evident that, wliile the offspring must receive from both ])arents 

 the matei'ial basis for the formation of the comolete color of the eye, 

 either the nmternal or ])aternal material must be prei)otent and ex- 

 clude the development of Die ot]i<n': the logical inference is that the 

 former activity replaces the latter ; but it is not uecessar\ that exclusion 

 from the cell chromatin should follow. TSTow, while some blends seem 

 to support the theory of fusion,, the sum total of facts of heredity are 

 H. Mis. 114 L'4 



