290 



PRODUCTION 0^ RACES AND SPECIES IN I^EPTINOTARSA. 



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.^ From the germ cells 



I 

 II 



HI 



IV 



VI 



VII 



VIII 



IX 



DECEMLINEATA 



10^ X 109 



DECEMLINEATA 

 48 (^, , 92$ 



Y 

 DECEivi LINE ATA 

 98(?, 1049 



10^ X 109 



DECEMLINEATA 

 67$ 



(Parent stock. 



After hibernatiou subjected to temperature averaging 9 above normal, E. H. 

 94% average for % reproductive cj-cle - % in normal condition. 



i 



DECEMLINEATA 

 74$, I 79$ 



DECEMLINEATA 

 61^, I 44$ 



DECEMLINEATA 

 48^, j 79$ 



DECEMLINEATA 

 88^, ,97$ 



DECEMLINEATA 



Killed 



DECEMLINEATA 

 45c?, , 45$ 



y 

 DECEMLINEATA 

 46<?, 74$ 



DECEMLINEATA 



31 



20$ 



DECEMLINEATA 

 12^, I 10$ 



DECEMLINEATA 

 92^, 74$ 



Not continued ow- 

 ing to lack of 

 room 



TORTUOSA /•crossed with $> 

 1 T^ I V^decemliueata / 



HYBRIDS /'decemlineataA 

 12(^1 17 Q Vdominant J 



TORTUOSA DECEMLINEATA 

 4j^. 3$ 11c?, r~-LL9 



TORTUOSA TORTUOSA HYBRIDS 

 6^,, 3$ 7^, I 9 24^, 31$ 



TORTUOSA TORTUOSA Kot couti- 

 1 ■) Cp nued ow- 

 * ingtolack 



10<^, 2$ 14^, 



Y 

 TORTUOSA I 



Killed in late 

 larval stage 



MELANICUM 

 10^, 13$ 



i 



MELANICUM 

 21 <^, ,19$ 



MELANICUM 



MELANICUM 

 14^, ^17$ 



MELANICUM 

 24^, 41 



MELANICUM 

 ~ ? 



Killed in late 



larval and pii- 



pjil stages 



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 decemlineata. 



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 



^ 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. 



