428 STELLA B. VINCENT 



of others or which makes it due to the pressure of numbers 

 because of breeding and the consequent lack of food in the 

 dry season; and (d) the sexual hormone theory. The article 

 closes with the following sentence. : ' The writer is familiar 

 only in a general way with the subject in hand and has merely 

 attempted to call attention to an aspect of migration which does 

 not appear to have been much discussed." 



Cooke (11) deals with the same subject, discussing the rela- 

 tion of weather to migration. From a series of records, extend- 

 ing in some instances over nine years, he makes a comparison 

 of the times of the arrival of certain birds with the weather 

 records of the same seasons. He is interested not only in the 

 time of the arrival but also in the probable effect of the weather 

 on the entire time of the migration. He tries to find out also 

 whether or not the weather of an entire season influences the 

 periodic flight, i.e., whether a long, cold winter or a prolonged 

 hot summer, either in the locality from which the birds come 

 or to which they go, affects the time of migration. He concludes 

 that the variations in the time of arrival from year to year do 

 not agree with the variations of the season, and that during the 

 spring migration the direction of the wind seems to have little 

 or no effect upon the arrival of the birds. 



A study of animal hypnosis is found in Mangold's (39) paper. 

 For his own experiments hens have served chiefly. He gives 

 Verworn's explanation of the phenomenon and cites much 

 experimentation with many animals. He attempts to connect 

 it biologically with that spontaneous immobility often seen in 

 animals, e.g., in the hen before the treading of the cock. 



LEARNING 



Szymanski (54) in a very carefully controlled series of experi- 

 ments tried to prove whether sound can serve as a stimulus for 

 movements in a definite direction with cats and dogs. He as- 

 sumed that Kalischer, Swift, Zeliony and others were right in 

 their assertion that dogs and cats can discriminate tones exactly. 

 The experiments were conducted in a dark chamber in a cellar 

 of the institute. The space used was 9 x 2.7 m. in size and was 

 lighted by an electric light hung from the ceiling directly over 

 the place of experimentation. The floor was covered with 

 linoleum and was washed every day with soap and water. For 



