242 ENTOMOLOGY 



periments upon the subject have given decidedly negative 

 results. Thus Weismann found that the amputation of the 

 tails of hundreds of mice, down to the nineteenth generation, 

 had no influence on the tails of the descendants. 



Mechanical injuries to the body of an organism are merely 

 casual, or accidental, effects of the environment and appear to 

 have no influence upon the germ cells. From the standpoint 

 of adaptation, injuries are only of minor importance. 



Functional Variations. While it is certain that the use 

 or disuse of organs affects their form in the individual, it 

 remains doubtful whether the effects of use and disuse are 

 transmissible. Weismann and his followers contend that they 

 are not. On the other hand, Neo-Lamarckians, as Cope, 

 Hyatt, H. F. Osborn, Packard and Eimer, have maintained 

 that they are. Weismann admits, however, that both use and 

 disuse may lead indirectly to variations, " the former when- 

 ever an increase as regards the character concerned is useful, 

 and the latter in all cases in which an organ is no longer of 

 any importance in the preservation of the species " ; and that 

 these variations may be acted upon by natural selection. 

 Thus, in a few words, the question stands. 



Environmental Variations. Under this head may be 

 classed such variations as are due directly to climate, nutrition 

 and other primary environmental influences. It is certain 

 that changes of temperature, light, and food, for example, 

 cause corresponding changes of form and function in the indi- 

 vidual organism; though the inheritance of these changes 

 directly induced by the environment is the subject of much 

 debate. 



Dallinger took flagellate infusorians that at first would die 

 at a temperature of 23 C, and by slowly raising the tempera- 

 ture through several years, brought them safely to a tempera- 

 ture of 70 C. There was some mortality, to be sure, in his 

 experiments, but other experimenters have obtained similar 

 results without the loss of a single individual, and therefore 

 it is important to note without the entrance of natural selec- 



