RECENT EXPERIMENTS IN HYBRIDISATION. 201 



Dresden produced seventy-five betularia (thirty S and 

 forty-five ? ) and ninety doubledayaria (thirty-four S and 

 fifty-six ? ). The male parent was doubtless an ordinary 

 betularia. Two of the examples classed as betularia 

 were darker than the normal, but otherwise no trans- 

 itional forms occurred. Standfuss is of opinion that even 

 these two need not be regarded as owing their darker 

 coloration to the cross, for it is well known that A. betu- 

 laria, like P. nwnacha, is undergoing a gradually increasing 

 melanism, which is probably protective, in many parts of 

 its area of distribution. The extreme aberration double- 

 dayaria, which thirty years ago was known only from 

 Great Britain, has now appeared in Westphalia, the Rhine 

 Provinces, Hanover, Gotha, and lastly in Dresden and 

 Silesia. In several of these places it is becoming more and 

 more common, and in at least some of them it is found side 

 by side with the darkening forms of A. betularia, which, 

 though of different nature and origin from the sport double- 

 dayaria, are no doubt being preserved and brought up to 

 its level (in aspect) under the influence of natural selection. 1 



10. Boarmia repandata L. S and do. ab. eonversaria 

 Hb. ? . A large brood raised from the eggs of a pair of 

 normal B. repandata contained three males and one female 

 of the aberration eonversaria. This female, which was paired 

 with a wild male B. repandata, produced twenty-eight re- 

 pandata (of which ten were males and eighteen females) and 

 six eonversaria (four being males and two females). The 

 majority of the larvae died during the winter. Here again 

 intermediate forms were entirely absent. - 



From the above experiments in the pairing of normal 

 forms with aberrations and local races, performed or recorded 

 by Standfuss, he arrives at the following conclusions : — 



1 Compare the facts with regard to Papilio Sarpedon given by Jordan, 

 ("On Mechanical Selection," Nov. Zoo/., 1896, p. 431) in illustration of the 

 position that " abnormal varieties show distinctly the directions in which a 

 species is able to develop ". Compare also the result of an experiment 

 cited by Tutt, " Melanism," 1891, p. 15. 



2 Compare the result of an observation by Mr. South, who raised 

 hybrids from the same two forms in 1883 (Proc. Ent. Soc. Lond., 1887, 

 p. xliv.). 



