250 Kansas Academy of Science. 



RaimanHia. and of Gager upon Chicgra, have shown that vari- 

 ous external influences, chemical and physical, acting upon or- 

 ganisms, can produce specific mutational changes in the germ 

 cells, and that these changes remain permanent through fu- 

 ture generations. 



From these permanent modifications we may pass to a class 

 of changes that are less fixed; that may be strengthened by 

 long subjection to these influences until they become more and 

 more definitely and permanently transmitted to future genera- 

 tions. The rather incomplete experiments of Woltereck upon 

 daphnians represent such cases. 



In other cases these influences may not originate characters, 

 but are merely capable of determining dominance of one over 

 the other when they are nicely balanced. Some of Tower's 

 experiments upon Leptinotarsa show this. Recent experi- 

 ments in the modification of the reproductive processes of 

 daphnians and rotifers likewise illustrate this principle. 



There is some difference of opinion regarding the nature 

 of these changes : but it appears to be very definitely shown in 

 the rotifers that parthenogenetic reproduction can be main- 

 tained an abnormally long time by exerting certain stimuli — 

 food (Xussbaum and Mitchell), waste products dissolved in 

 the culture medium (Shull). etc. These measures prevent the 

 development of male-producing females. It has been shown 

 that these are really sexual females, which, if impregnated, 

 produced winter eggs that develop into females. Morgan, 

 Shull. Whitney and others have urged that these influences 

 determine whether there should be a parthenogenetic or sexual 

 phase of reproduction : but as Mitchell has pointed out. this is 

 a change from a condition in which regular parthenogenetic 

 (unfertilized) eggs produced females to one in which eggs 

 capable of being fertilized produced males in the absence of 

 fertilization. 



While these external influences are very potent when the 

 egg is susceptible, it has been shown that they cannot over- 

 come certain internal factors that make for sexuality in cul- 

 tures that have passed through many parthenogenetic genera- 

 tions. 



Equally striking results were attained by Woltereck in 

 daphnians. He found that meager feeding, and. indirectly, 

 temperature, tend to produce sexuality in these forms. 



