PREFATORY NOTE. 



The investigations, the results of which are herein set forth, have been 

 carried out by aid from the Elizabeth Thompson Science Fund, in the collec- 

 tion of the data of distribution and migration of L. decemlineata and in some 

 of the earlier experimental work upon the same species, and by certain grants 

 from the University of Chicago and from the Carnegie Institution of Wash- 

 ington, which have made possible experimental study in the tropics. I 

 desire to express my deep sense of obligation to all these for the aid rendered. 



The investigations have been conducted in the Museum of Comparative 

 Zoology in Cambridge, in the Biological Laboratory of the Brooklyn Insti- 

 tute of Arts and Science, at Cold Spring Harbor, and in the Hull Zoological 

 Laboratory of the University of Chicago ; and to the directors of these 

 institutions and their staffs I am under great obligation for much kindly 

 advice and valuable criticisms. 



The experimental studies presented in this contribution, with the excep- 

 tion of three small experiments, were brought to an end in July, 1904. 

 Through the carelessness of workmen engaged to attend to the heating plant 

 of the university, on the hottest day of the season steam was turned on in 

 full force in the greenhouse where my experiments were, terminating at 

 once the series of experiments and cultures which had been carried with 

 great labor and expense through several years. These cultures have been 

 started again and are now being continued at Chicago and in the tropics of 

 southern Mexico. 



Ill 



