THE PHENOMENA OF REVERSION 319 



only occur eis^ht times successivelv, two of the unmodified 

 ancestral idants being added each time to those already pres 

 ent, in order to produce a germ-plasm consisting of pure ances- 

 tral idants, and the organism developed from it would then 

 agree with the ancestor in question in all its characters. Under 

 particularly favourable circumstances the process might even 

 be completed in four generations, as is shown in the following 

 table : — 



^ .-if a', b, c, d e, f, g, h = ^ germ-cell. 



Generation I. -' , . , , & ^^ ,, 



\ a', i, k, 1 



^ ^. TT ^ a', b, a', d 



Generation II. - , ' 



i a', q, a', s 



Generation III 



m, n, o, p = 9 " 



c, i, k. 1 = ^ " 



t, u, V, w = 9 " 



b, d, q, s = Z '^ 



a, /?. 8, e = 9 



Generation IV. - , , ^' ^ ^ / / / _ o 

 (a^ a^ a^a<a^a,a^a — q; 



u 



The letters in the above table indicate the idants, which — 

 with the exception of a', which represents the unmodified ances- 

 tral idant, and only occurs once in the first generation — are 

 only individually different from one another. The vertical line 

 represents the reducing division of the mother-germ-cell, which 

 in the most favourable case we are now^ considering, always 

 causes this ancestral idant a' to pass into the germ-cell about 

 to undergo amphimixis. For the sake of simplicity, the con- 

 jugating germ-cells are assumed to be similar in respect to 

 their contained ancestral idants. It would thus follow that 

 germ-plasm consisting of ancestral idants only, would be pro- 

 duced in the fourth generation. 



Although we must certainly admit that so favourable a com- 

 bination of events can hardly ever occur, it cannot be doubted 

 that an accumulation of ancestral idants may take place in one 

 germ-cell in the course of a large number of generations, and 

 that a jfiajority of these ids may consequently come together 

 in fertilisation. In this case a more or less complete reversion 

 to the ancestral form must take place. As such reversions to the 

 complete type of the ancestral species cannot be observed to 

 occur in the normal reproduction of pure and long-established 

 species, we must conclude that all the idants Juwc become 

 niodijied in such old and pure species, each of which produces 



