TOWER'S EXPERIMENTS ON BEETLES 159 



blastogenic and many so-called fluctuating variations may also 

 perhaps belong to the same category. 



The modifications of the germ cells by virtue of which the 

 offspring come to differ to a greater or less extent from their 

 parents are, as we have seen, often attributed in large 

 measure to permutations and combinations of different characters 

 which take place in the sexual process (amphimixis) and the 

 preceding nuclearreduction. It has long been suspected, how- 

 ever, that thegerm cells themselves, apparently independently of 

 the body in which they are enclosed, may be influenced by the 

 environment to which arc-animal or plant is^ exposed, and the 

 observations of Tower 4 upon beetles 'of the genus Leptinotarsa 

 may be referred to in this 'connect ion. 



This observer considers that all permanent variations in these 

 beetles, so far as can be discovered, arise in the germ cells and 

 are in no wise the results of inherited somatic modifications. He 

 attributes their appearance to the direct action of the environment 

 upon the germ plasm and supports his views by a series of very 

 interesting experiments. He subjected the parents to environ- 

 mental stimuli of various kinds during the growth and matura- 

 tion of their germ cells, and then, after the ova had been fertilized, 

 allowed the development of the young to take place under normal 

 conditions. The parents, having already reached their final state, 

 were not themselves visibly affected by the stimuli, but a large 

 percentage of the offspring showed surprising modifications 

 which were strictly inherited. These modifications appear to be 

 in no way adaptive. They seem to bear no relation to the nature 

 of the stimulus which calls them forth and to be of no value to 

 the organism in the struggle for existence. 



We may cite one example of Tower's experiments. Four males 

 and four females of Leptinotarsa decemlineata (the potato beetle) 

 were exposed during the earlier part of the laying period (the 

 eggs being matured and laid in successive batches) to extremely 

 hot, dry conditions accompanied by low atmospheric pressure. 

 The eggs were removed as soon as laid and reared under natural 

 conditions. From 506 larvae thus reared 96 adult beetles were 

 obtained, of which 82 were of a form known as pallida, 2 of a form 

 known as immaculothorax, and the remainder unmodified. During 



1 "An Investigation of Evolution in Chrysomelid Beetles of the Genus Leptino- 

 tarsa," by William Laurence Tower. (Publications of the Carnegie Institution, 

 Washington, 1906J 



