6 PREFACE. 



of new problems on bird activities in general, and furnishes methods which 

 may acquire a usefulness much wider than their present connections. 



Our experiments and conclusions on homing proper will be found on pages 

 59 and 60. These results, while not settling the ciuestion of the sensory 

 mechanism by means of which the birds return to the nests, do remove all 

 doubts about the fact that the noddy and sooty terns can return from distances up 

 to 1,000 miles in the absence of all landmarks (at least in so far as the term 

 landmark is understood at present). The problem of homing has thus become 

 defined, and exj^crimental work of a definite kind is needed for its solution. 

 The paper on vision in birds (p. 87) seeks to gain some insight into the question 

 as to whether the birds have any s])ecial visual equipment (such as infra-human 

 sensibility to rays of light, sensitivity to infra-luminous rays, etc.) which 

 might be employed by them in finding their goal. This paper mai'ks only 

 the beginning of the research into the sensory mechanism possibly used by 

 birds in homing. So far we have not been able to locate the sensory factors 

 used in return, but we are far from being without hope that future studies 

 may yield results which will enable us to solve the riddle which ha.s been pro- 

 pounded to scientific men of all ages, but as yet never satisfactorily answered. 



The final paper by Dr. Lashley, on the acquisition of skill in archery, 

 has of course no connection with the work on homing. Its inclusion in the 

 present volume is made desirable by the fact that the work was begun at 

 Tortugas under the same arrangements that were made for the other investi- 

 gations. 



Both Dr. Lashley and I wish to express our thanks to Dr. A. G. Mayer, 

 Director of the Marine Biological Laboratory, for his generous assistance in 

 these investigations. 



John B. Watson. 



The Johns Hopkins Univeksity, 



February 1915. 



