112 



Experimental Evolution, Variation, and Heredity 



Part III deals with the linkage in rats of three genes in one linkage system, 

 and with the linkage in mice of two genes apparently corresponding with two 

 of those which are also linked with each other in rats. 



No. 263. 



TOWER, W. L. The Mechanism of Evolution in Lepti-' 

 notarsa. Octavo, vin+1-340 pages, 19 plates, 156 

 figs. 



(Appendix.) BREITENBECHER, J. K. The Relation of 

 Water to the Behavior of the Potato Beetle in a 

 Desert. Octavo, pp. 341-348, 5 figs. (Not sold 

 separately.) 



Published 



1918. 

 Price $8.00. 



The data and conclusions presented in part by Dr. Tower are the product of a 

 project in which it was attempted to attack the "evolution problem" in one set of 

 organisms from a number of different aspects. Evolution in organisms must be 

 conceived of as the product of the interaction of internal and external factors, 

 operating in strict mechanistic manner, as in non-vital phenomena, so that the 

 central problem was the determination and proof of the mechanism of action of 

 these two groups of factors whose operations are productive of evolutionary 

 changes. Experimental analysis of the problems, prosecuted with rigor and thor- 

 oughness, has been held to be the only means of progress. The basis of all 

 methods of change is found to be directly the product of the nature of the genetic 

 factors of composition and their capacity for diverse modes of reaction, especially 

 with factors of the environic complex. Purpose, utility, and kindred concepts 

 have found no support, every change appearing as the chance mechanistic product 

 of the reacting agents ; while the product of the reaction either was able or not 

 able to operate under the conditions of origination, so that survival is decided at 

 once and not after long and faltering trials. 



During the course of the experiments considered by Dr. Tower it was observed 

 that soil-moisture, humidity, and the like played an important role in modifying 

 the activities of these organisms when introduced into the arid region. Dr. 

 Breitenbecher, therefore, undertook a series of investigations to discover any pos- 

 sible connection between this water-relation and the reactions of the potato beetle, 

 Leptinotarsa decemlineata, when transplanted into the desert from a temperate 

 habitat. A large stock of this species was sent to Tucson from Chicago in June, 

 1911, so that comparative studies under different environmental complexes could be 

 made. Three cultures were established in several open-air breeding-cages. Two 

 of these stations were arid in character, while the third was temperate. The 

 biological significance of conditions at the stations is given and the problems dealt 

 with concern the relations which exist between the activities of the beetles when 

 allowed to reproduce at these localities and the changes produced in the water- 

 content of the animals through the action of the various environmental factors. 



