294 



PRODUCTION OF RACES AND SPECIES IN I.EPTINOTARSA. 



when the differentiation of the germ plasm begins and preparations are made 

 for the following generation, that these changes are easiest to bring to pass. 



EXPERIMENTS WITH I.. UNDECIMI.INEATA. 



Living material of L. imdecimlineata from Orizaba, Vera Cruz, Mexico, 

 brought to Chicago in August, 1904, and reared in September and October, 

 was, after hibernation, subjected, during the growth of the germ cells, to an 

 extreme stimulus of high temperature, 10° C. above the average, and a rela- 

 tive humidity of 40 per cent, with the result that out of the 190 eggs laid there 

 emerged 11 beetles, all of the form angiistovittata. They were reared, and 

 gave pure progeny. 



.GENERATIONS 

 I 



n 



III 



IV 



V 



VT 



UNDECIMLINEATA 

 80 J', I 190 9 



UNDECIMLINEATA 



74 J^: 



829 

 4<? 



Orizaba, V. C, Mexico, August, 1904. 



Eeared afc Chicago and aestivated. 

 4 9 Subjected to experiment. 



UNDECIMLINEATA 

 38^; (42 9 



UNDECIMLINEATA 

 60<?, j 719 



Continued at Chicago 

 as brood living free 

 upon plants in green- 

 house. Continued to 

 breed true without giv- 

 ing anymore anguato- 

 vittata. 



ANQUSTOVITTATA 

 &$, l59 



ANQUSTOVITTATA 



14^, I 239 ( .iEstivated in February, taken to Mexico in March. 



ANQUSTOVITTATA 

 36^, [349 



ANQUSTOVITTATA 



92^, 98 9 (Now aestivating. Jan., 1906. 



Text-figure 30. 



I 



As far as was discovered in these cultures of L. undecimlineata the results 

 of the experiment in the stimulation of the growing germ cells were the same 

 as those obtained in the ohers experimented with, namely, permanent varia- 

 tions, which bred true to type. 



CONCI^USION. 



I have presented in these few pages some results obtained in a line of 

 investigation which is as yet in its infancy and which is being actively contin- 

 ued. Besides the experiments given, I have tried and am continuing other 

 experiments upon the same species, as well as upon other species of the genus 

 Leptinotarsa and species in closely related genera. Of this experimental work 

 I introduce here only my longest continued and clearest examples as part of 

 the argument for the method of evolution which I believe is followed in 

 insects. I shall present in some future report a full statement of these experi- 

 ments, and at that time shall be able to go more completely into the details 

 and theoretical aspects of the problem. Herein, however, I shall be content 

 to make a simple statement of the results, reserving theoretical consideration 



