286 PRODUCTION OP RACES AND SPECIES IN LEPTINOTARSA. 



development of extreme variations, is associated with, if not due to changes 

 in the environmental complex in different directions from the mean or average 

 conditions. In the light of this converging evidence, it will not be unfair to 

 draw the conclusion that these variations, which are shown in my cultures to 

 be true factors in the formation of races and species, are due to the relations 

 existing between the parent species and the changed environmental complex. 

 The phenomenon is a natural one and not due to agencies or causes not 

 capable of investigation. I have planned and carried out, in the years 1S99 

 up to date, a series of experiments and cultures to test and further elaborate 

 this tentative hypothesis, reached as the result of pedigree culture, observa- 

 tion, and study of these beetles in nature. I shall give in the next section 

 some of the experiments, their results, and the conclusions arrived at ; after 

 their presentation we shall be in a better position to discuss the general results 

 derived from this series of cultures and experiments. 



EXPERIMENT IN PRODUCTION OF NEW CHARACTERS AND SPECIES. 



I have shown that, as far as can be discovered, all variations of permanency 

 in these beetles arise in the germ cells and are in nowise the result of 

 inherited somatic modifications. This point is so repeatedly demonstrated in 

 my experiments with these beetles that I have come to regard the somatic 

 origin of permanent variations as untenable until we have experimental proof 

 of its existence. The origin of germinal variations in these beetles appears 

 to be correlated with environmental changes, and I have repeatedly noted the 

 appearance of permanent variations in nature and in experiment where there 

 was a wide deviation in the factors of the environmental complex. I there- 

 fore, some years ago, came to the conclusion that the environment did not act 

 in any specific manner, but solely as a stimulus, which, when brought to bear 

 upon the germ plasm, produced a response or change which took the form of 

 permanent variations in some one or more characters. To test this hypothesis 

 several sets of experiments were begun in the year 1899, continued to the 

 termination of my series in 1904, and started again in 1905. 



In these experiments I followed the plan of subjecting the parents to envi- 

 ronmental stimuli during the growth and maturation of the germ cells, and 

 then, after fertilization, of allowing the subsequent development to take place 

 under normal conditions. The beetles emerge from the pupa or from the 

 winter hibernation with the germ cells in an undeveloped condition, and these 

 undergo their development, especially the ova, during the few days following 

 emergence. None of the beetles develop all their eggs at once, as do the 

 Lepidoptera and many other insects, but in batches, each batch being laid 

 before the next begins development, so that between the laying of each two 

 batches there is an interval of some four to ten days. All of the beetles in 



