90 HOMING AND RELATED ACTIVITIES OF BIRDS. 



It can readily be seen that the box offers two alleys which lead into food com- 

 partments, F and Fj. Two doors, D and D t , permit one to confine the animal 

 in the proper food compartment. By a special mechanism the doors can be 

 closed after the passage of the animal from without the apparatus by pulling 

 knobs K and K^ Two doors lead from F and Fj into H. It is thus possible 

 to work with the animal without touching it and without being seen by it. 



By means of a special signaling device the movements of the animal can 

 be recorded without the necessity of watching it. Two miniature lamps, 

 blackened except for an opening about 1 mm. in diameter, are electrically 

 connected with the platforms S and Sj and S 2 . When the animal crosses S 

 and goes into the response chamber both lamps are caused to wink (break 

 circuit). If he then crosses the right-hand platform S 2 , the right lamp goes 

 out until the reaction is completed and the animal turns into R. If the animal 

 goes across S^ the left lamp goes out, etc. In the drawing the stimulus light 

 falls upon the right stimulus patch X; consequently food may be obtained by 

 passing around R through the open door D!. It will be noted that the door D 

 is closed. If the animal makes the wrong choice it must pass S 1; around into 

 alley L; there finding the door closed, it must retrace its steps and pass S 2 , 

 into R through D. The apparatus as a whole can be shifted so that the light 

 may be made to fall either upon X or X : at will. Although arranged for pun- 

 ishment by electric shock, punishment was not used in the experiments upon 

 the chicks. 



THE LIMITS OF THE CHICK'S SPECTRAL SENSITIVITY. 



The experiments were carried out upon three chicks. Experimentation 

 began on August 30, 1912. On that date the chicks were exactly 30 days of 

 age. Before actual tests were made the animals were forced to go through the 

 complete reaction they would have to use during regular experimentation; that 

 is, they were at first confined in the home box, then admitted to the reaction 

 chamber, and then forced to go to the right or left food compartments at the 

 will of the experimenter. These preparatory exercises were conducted in a 

 well-lighted room. One of the interesting things appearing in these tests with 

 both chicks and terns was the failure of the birds to learn readily to pass 

 around into the alleys L and R. Some rats which the writer tested in the same 

 way learned to make these turns in a few trials. It took nearly 3 weeks to get 

 the birds to run rapidly from entrance into the stimulus chamber around to 

 the food. When they had learned to make the turns, regular tests were begun. 

 These consisted in responding positively to the compartment illuminated by 

 the monochromatic light (or negatively to the dark compartment). 



The chicks were brought into the dark room in a basket and allowed to 

 remain in complete darkness for 10 minutes. Then a 16 c. p. tantalum light 

 placed 1 meter above the center of the home box was turned on and a chick 

 was placed in H. The chicks are designated by D, R, and G. D was always 

 experimented upon first; then in order, R and G. The state of adaptation for 

 the three chicks was thus not quite the same.* As soon as a chick was placed 



*And yet no marked differences in sensitivity of a progressive kind were noted. The use of 

 the white light after every response, as above described, probably kept adaptation constant in 

 all. The two chicks not undergoing experiments were kept in the room with the apparatus. 

 The wicker basket in which they were confined admitted light with readiness. 



