PEDiGRi:^: bre:e:ding. 



281 



ruination of my experiments in July, and were carried over into 1905, giving 

 after transfer to Mexico in March, 1905, a Mendelian splitting into typical 

 riihrivittata and hybrid forms (text-fig. 22). These .were separated and 

 reared. The pure cultures of rubrivittata showed as the result a new charac- 

 ter, namely, that its life history as well as less important characters were 

 changed, there being three generations in its yearly cycle instead of two, as in 

 the parent species, and in all the species in its immediate ancestry. 



This change in the life cycle fromi hibernating in every second generation, 

 as do most of the species in the genus, to hibernating in every third, is 

 striking and significant, the three generations being gone through in about 



.GENERATIONS. 

 I 



n 

 ni 



IV 

 V 



VI 



VII 



14^, 329 DECEMLINEATA McPherson, KaiiBas. July, 1903. 



DECEMLINEATA 

 46 $, Ml2^ 



DECEMLINEATA 

 38^, J 52 



DECEMLINEATA 

 91^, 829 



reared at Chicago, hibernated. 



RUBRIVITTATA - crosfed with modal Q from Chicago. 



HYBRIDS 



19<?J219 hibernated. 



RUBRIVITTATA HYBRIDS 

 6(J. 1 49 28^^,1279 



RUBRIVITTATA HYBRIDS 

 11^.1 109 35<^| 409 



RUBRIVITTATA T 



38 J^, I 309 



In hibernation, RUBRIVITTATA 

 Oct., 1905. 68 J, I 709 



In hibernation, Nov., 1905. 



Text-figure 22. 



JRI\ 



H 



(Rl\ 



RUBRIVITTATA 

 14^,1 189 



RUBRIVITTATA 

 48 ^, I 46 9 



In hibernation, Oct., 1905. 



the same time as the two of the parent species. The cultures with rubrivittata 

 demonstrate clearly that changes in physiological characters can take place 

 rapidly^ as do changes in structure, and that these changes may alter not only 

 unimportant characters, but a most fundamental one as well. We shall have 

 occasion to consider a similar case even more striking and interesting in a 

 later part of this chapter. 



With the variations albida, minuta, defectopunctata, and immaculothorax 

 found in nature, I have succeeded in obtaining cultures for one or two gener- 

 ations only, and these I shall not dwell upon, since they add only slightly to 

 this account. We shall, however, meet with these in the experimental pro- 

 duction of extreme variations, where it has been possible to get cultures, 

 owing to the greatly increased number available for experimentation. 



With these variations from nature and the cultures made from them, it is 

 conclusively demonstrated that there do appear in nature rapidly developing 

 extreme variations which stand apart from the normal fluctuating variations 



