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THE AMERICAN NATURALIST [Vol. XL V 



to accurate measurement. Qualitative differences, such 

 as those of color or of physiological reactions, do not 

 seem well adapted to such experiments, although they 

 have commonly heen the ones dealt with in studies of this 

 sort. 



In the second place, we must choose such an organism 

 and such a physical agency that the latter may act upon 

 the former without immediately influencing the germ- 

 cells. This would seem to rule out of consideration as 

 really crucial tests of this problem all experiments, how- 

 ever instructive otherwise, in which modification has been 

 brought about through the influence of foods, unusual in 

 amount or in character. For the effect of these upon the 

 parent body is, of course, a chemical one, and the specific 

 substances responsible for the modifications are presum- 

 ably free to enter the germ-cells. The experiments of 

 Arnold Pictet upon lepidoptera and of Houssay upon 

 fowls are to be recalled in this connection. Similar con- 

 siderations apply with equal force to any results from 

 experiments in which invertebrate animals or " cold- 

 blooded" vertebrates have been influenced by tempera- 

 ture. The recent work of Kammerer upon lizards 4 and 

 that of various investigators upon butterflies and moths 

 occur to us at this point; likewise certain features of 

 Tower's work on Leptinotarsa. In such cases, by pretty 

 general consent, we have to do with an " immediate effect 

 upon the germ-plasm," and not with transmission at all. 

 Later, I shall inquire a little into the validity of this 

 assumption. 



In the meantime, I will point out that for certain 

 classes of animals this objection cannot be raised, at least 

 in its original form. I refer to the so-called * 4 warm- 

 blooded ' ' ones. I am not very well versed in that branch 

 of physiology which deals with temperature regulation, 

 but the published evidence which I have examined seems 

 to show that mammals normally undergo but slight fluc- 

 tuations of body temperature as a result of even very 



'Archiv fur EntwicUungsmechanik der Organismen, September, 1910. 



