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THE AMEBIC AN NATURALIST [Vol. XL VIII 



Lutz for Professor Loeb, included by mistake some flies 

 heterozygous for these two characters; for in our very 

 extensive experience with wild stock from Cold Spring 

 Harbor (the origin of most of Dr. Lutz's stock) and else- 

 where these mutants have never arisen again. 



At various times experiments have been made in this 

 laboratory involving wide ranges of temperature, 3 salts, 

 sugars, acids, alkalis without any resulting mutation. 

 In fact, our experience with Drosophila has given us the 

 impression that mutations are rare events, although the 

 actual number of our mutants is now quite large. 



Guyenot 4 also has treated ampelophila to high tempera- 

 tures, to radium and to X-rays without result. When the 

 adult flies were treated with ultra-violet light, however, a 

 definite type of " black" fly was obtained. The first eggs 

 that such females lay are normal and give rise to normal 

 flies. The eggs laid later fail to hatch, although they ap- 

 pear to begin their development. On the third day 

 amongst the abnormal eggs some were found that gave 

 rise to flies that were apparently normal. It happened 

 that they were not examined again until after the flies of 

 the next generation had appeared (many of them had 

 died). Both among the living and the dead flies there 

 was a considerable percentage of black flies. The black 

 females laid eggs which did not develop, even although 

 normal males were added. Why the black males were not 

 also tested by outcrossing is not apparent. The descrip- 

 tion of the black flies given by Guyenot tallies in some 

 points with our stock of ebony in which the females were 

 at first usually infertile but the males fertile. At first, 

 indeed, we kept the stock by breeding the ebony males to 

 the heterozygous females. These are intermediate in color. 

 In fact, Guyenot seems to have had heterozygous flies but 

 did not, according to his account, obtain any black flies 

 from them. However, if the ultra-violet light is a specific 

 agent for these mutations the experiment can easily be 

 repeated. 



3 Science, XXII, 1910. 



iBull. Scientifique, XLVIII, 1914. 



