RECENT EXPERIMENTS IN HYBRIDISATION. 197 



as to the effect of crossing a sport or aberration with its 

 parent form. The result, which is entirely different from 

 that which follows the crossing of distinct species, or even 

 of local races, may be broadly stated as follows : When an 

 aberration is crossed with its parent form the issue is 

 sharply divided, in both sexes, into specimens of the aberra- 

 tion and of the normal form of the species. 



Thus in the dark aberration zatima Cr. of Spilosoma 

 lubricipeda Esp., there are many degrees from the least 

 dark form of the aberration (ab. intermedia Bang- Haas) up 

 to the darkest (ab. deschangei Depuis) ; but no transitional 

 forms occur to bridge over the wide gap between intermedia 

 and lubricipeda, nor can they be produced by crossing these 

 two. "It seems," so Standfuss expresses it, "as if there 

 were antagonistic characters which cannot coexist in the 

 same individual ". 1 Instances follow which will be briefly 

 noticed here. For full details, which are of great interest, 

 the reader is referred to the Handbuch, pp. 305-321. 



1. Spilosoma lubricipeda Esp. $ and do. var. zatima 

 Cr. 5. These, crossed by Burckhardt in 1889, gave lubrici- 

 peda, intermedia and zatima [intermedia being, as just stated, 

 merely a less dark form of zatima). Two of these intermedia 

 were paired, giving again lubricipeda y inter7nedia and zatima. 

 In this third generation several pairings were effected, as 

 follows : zatima <S and lubricipeda ? ; lubricipeda $ and 

 zatima ? ; intermedia $ and do. ? ; intermedia $ and 

 zatima ?'. All these gave lubricipeda, intermedia and 

 zatima in varying proportions, except the cross lubricipeda 

 $ and zatima ? , from which only zatima resulted. A pair 

 of lubricipeda from this fourth generation gave a brood of 

 34 lubricipeda and 1 extreme zatima. 



In all these successive broods, carried on into the fourth 

 year from the date of the original pairing, there were no 

 transitional forms between lubricipeda and intermedial 



x The bearing of this may be noted on the theory of " determinants". 

 See Weismann, Germ-plasm, 1893, pp. 293, etc. See also Bateson, Ma- 

 terials for the Study of Variation, 1894, es P- Intro., Sect. iii. ; and this 

 Review, 1897, pp. 554"5 6 9- 



- The above case of cross-breeding between colour-varieties of the same 

 race, in which there are no intermediates and the colours of the ancestors 



