ACQUIRED CHARACTERS 35 



Europe, is willing to accept at full face value such cases as 

 this brought forward by Fischer, and to allow that the race 

 may become darker through long-continued subjection to 

 lower temperatures. He supposes not that the body effects 

 are transferred to the germ-cells, but that the low tempera- 

 tures act simultaneously on the body and on the germ-cells, 

 producing in them similar changes, the changes in the germ- 

 plasm affecting the hereditary character of the race per- 

 manently. This view under the name of ^parallel-induction 

 now has many adherents. It is a practical admission for a 

 particular case of the Lamarckian principle of evolution 

 guided in its course by environmental action. Whether, 

 however, Weismann is right in his interpretation may still 

 be regarded as an open question. 



In this country, W. L. Tower (1896) has carried on exten- 

 sive experiments upon potato beetles and related insects, in 

 which variations in temperature and humidity of the environ- 

 ment have been followed by variations in pigmentation of the 

 insects, similar to those observed by Fischer in the case of 

 butterflies. Tower interprets his observations, as would Weis- 

 mann, as showing, not inheritance of acquired characters but 

 direct modification of the germ-cells, independently of the 

 soma. For, he claims to have obtained modification of the 

 germ-plasm, which accordingly resulted in inherited varia- 

 tions, where no parallel modification of the body of the parent 

 had occurred. Inheritance of an acquired character is accord- 

 ingly excluded because no modification was acquired. His 

 strongest evidence for this claim consists of cases in which 

 the same parents were subjected to periods of heat or cold, 

 alternating with periods of normal temperature, each being of 

 several weeks' duration. It was found that when a batch of 

 eggs was produced in or immediately following a period of 

 heat, characteristic color variations were likely to occur 

 among the offspring which may be called heat variations and 

 these proved hereditary. But when eggs were produced by 

 these same parents at normal temperatures, no such varia- 

 tions occurred. Similar effects were obtained in cold periods. 



