186 LECTUEES ON BIOLOGY 



developed tails, this experiment was thought to have furnished 

 a conclusive proof against the transmission of acquired characters. 

 It is, however, hardly possible to imagine a more naive experi- 

 ment, for there can scarcely anyone be found to believe that 

 the loss of an organ takes place in Nature in such a rough and 

 ready manner. That external injuries of parents are not trans- 

 mitted to the children should be accepted a priori without any 

 such experiments. Moreover, we can on this point refer for a 

 proof to a far greater experiment. Though circumcision has 

 been practised among the Jews on an enormous scale. for several 

 thousand years, nothing has ever been heard of the foreskin 

 having, as a result of the operation, begun to atrophy or become 

 degenerate. In another case, however, it seemed as if under 

 certain circumstances injuries, or at least their consequences, 

 are transmissible. Thus Brown-Sequard contended that epilepsy 

 caused in guinea-pigs by severing the Nervus sciaticus had 

 actually been transmitted to the descendants. Later experiments 

 made by Sommer have, however, cast some doubt upon Brown- 

 Sequard's observations, so that in the absence of corroborative 

 evidence we are compelled to disregard them. 



The classic instance of the transmission of acquired charac- 

 ter are the important experiments made by Weismann, Fischer, 

 Standfusz, and others, with butterflies. Fischer selected the Tiger 

 moth (Arctica caja), and fed a large number of young cater- 

 pillars on white dead-nettle and dandelion, their ordinary food- 

 plants. One hundred and two caterpillars reached the pupa stage. 

 For purposes of control, some of these pupae were kept under 

 normal conditions and produced normal butterflies ; the rest, 

 were exposed intermittently to a temperature of 8 C. The 

 result of these unusual conditions, which were well sustained 

 by the pupae, was most remarkable. The emerging butterflies, 

 forty-one in all, were considerably darker than their normal rela- 

 tives ; in particular the brown or black spots or stripes on the 

 anterior and posterior wings were much larger. It seems plain 

 that these changes were the direct consequence of the effects of 

 the cold to which they were exposed during the pupa stage. 



Fischer now selected among these butterflies a male possessing 

 this variation in a strongly pronounced form, and paired it with a 

 female exhibiting the characteristic in a similarly pronounced 



