290 



PRODUCTION OF RACES AND SPECIES IN LEPTINOTARSA. 



constant from the start, showing in the fourteen generations no tendency to 

 revert to the parental standard. As far as I can discover, this case can be 

 explained only as the direct response of the germ plasm to the extreme stimuli 

 used in the experiment. It seems impossible to account for the condition pro- 

 duced upon the basis of a latent character of this kind somewhere in the 

 ancestry of this genus. Moreover, all the beetles in this experiment had an 

 equal chance to be accelerated by the conditions of existence, so that this 

 factor could not by any stretch of the imagination be held to account for the 

 development of this change. As far as is known, the only changed factor in 

 this experiment was that used in the third generation upon the 7 males and 7 

 females for three-fifths of the reproduction period. 1 From the germ cells 



GENERATIONS, 



I 

 II 



III 



IV 



"V 



VI 



VII 

 VIII 



IX 



DECEMLINEATA 



10 <? x 109 



tr 



DECEMLINEATA 

 48<?, 92$ 



+ 

 DECEMLINEATA 

 98<?, 104? 



10,? X 10O 



\ 



DECEMLINEATA 

 80 J 1 , | 67? 



(Parent stock. 



After hibernation su 

 'Ji y o average fur : - 



jected to temperature averaging n above normal, E. H. 

 reproductive cycle- % in normal condition. 



I 



DECEMLINEATA 

 74<?, 1 799 



DECEMLINEATA 

 6'c?, 1 44$ 



DECEMLINEATA 

 48 , J 79 9 



DECEMLINEATA 



88<J, . 979 



DECEMLINEATA 

 Killed 



DECEMLINEATA 



45 c? , 45 9 



i 

 DECEMLINEATA 



46 <?, 749 



y 



DECEMLINEATA 

 31c?, 1 209 



DECEMLINEATA 

 12,?, j 109 



DECEMLINEATA 

 92<J\ 749 



Isot continued ow- 

 ing to lack ul 

 room 



Arro 

 l^dec 



Bed ,\ ith 

 cemlineat 



? ) 



TORTUOSA 

 4c?, 39 



V 

 TORTUOSA 

 6^ 39 



TORTUOSA 

 10,?, 2 9 



ORTUOSA 



Killed in ]te 

 larval stage 



/'decemlineataA 

 Idominant / 



DECEMLINEATA 

 11<?. I L79 



TORTUOSA 

 7 <?'| 9 

 TORTUOSA 

 14 c?, 119 



Died 



HYBRIDS 

 24,?, 319 



111:' In M h 



oj room 



MELANICUM 

 10c?, 139 



4 



MELANICUM 

 21c?, .19 9 



V 

 MELANICUM 

 Bff. ^49 



MELANICUM 



u$, ^179 



MELANICUM 

 24 <?, 41 9 



MELANICUM 



Killed ill late 

 larval ;,:, I pu- 

 pal Btagos 



Text-figure 27. 



subjected to stimuli this race arose, but not at once, two generations being 

 necessary in which to disentangle the changed characters from the non- 

 modified dcccmlincata. 



The forms immaculothorax and albida produced in this experiment were 

 reared through three and two generations respectively, but were weak, ill- 

 adapted variations, and were kept alive only by closest attention. Although 

 these variations have arisen many times in my experiments, they are never 

 strong, nor do they produce many eggs, but die quickly. When they do 



1 The fact, clearly shown in this experiment, that the response (modification) does not 

 always follow the stimulus at once, but may not appear for some generations, is a point 

 of great moment. It shows that the appearance of a "mutant" must not be attributed to 

 "internal forces" unless we are able to say that there has not been a previous stimulus 

 due to changed environment, habits, etc. 



