BEHAVIOR OF VERTEBRATES 441 



of attack is a random one (" Probiermethode "). The problem 

 is not learned by one successful solution, but by many repeti- 

 tions. During the learning process involuntary attention is 

 withdrawn more and more from the goal, and is directed toward 

 the method of arriving at the goal. Changes in the arrangement 

 of the apparatus call out new trial movements. Check experi- 

 ments (" Vexierversuche ") following too closely upon one 

 another tend to break down the reaction. 



The author makes a distinction between sensory and motor 

 reactions which is not clear to the reviewer. He says that motor 

 reactions predominate, and that sensory reactions are called out 

 only by some external demand (" aussere Notigung "). If the 

 external demands are continuous and compelling, the dog can 

 accustom himself to the sensory reaction. I presume this state- 

 ment refers to the fact that the dog can learn to discriminate 

 between the different cords, strings, etc., used in the experiments. 



His conclusions concerning the general levels of intelligence 

 of the dog are not far removed from those of Thorndike. The 

 dog shows no e\'idence of reflection. There was little evidence 

 even of sensory thought (" Nur in einigen wenigen Versuchen 

 aussert es sinnliches Denken, das allerdings bis zu einem gewissen 

 Grade einer Erziehung fahig ist.")* 



Birds. Herrick,"^ in an admirable study of the young and 

 adult cuckoo, largely increases our knowledge of the first appear- 

 ance, the development, and method of functioning of instincts 

 in birds. The paper shows quite clearly how much valuable 

 w^ork can be done by a study of animals in their natural environ- 

 ment. The instinctive activity of the birds studied is too com- 

 plex and detailed to be reviewed fully. The author's especial 

 interest centers about the peculiar instinct in the adult cuckoo, 

 to lay its eggs in the nests of other birds. Herrick would find 

 the origin of " parasitism " in many of the old world cuckoos 

 and in the American cow-bird, in the disturbance of the cyclical 

 reproductive instincts; in particular, that of the attunement of 

 egg-laying to nest-building. This maladjustment shows itself in 

 the laying of the eggs before the nest is ready to receive them, and 

 in laying them at very irregular intervals. For example, the 



* It is somewhat surprising that an important psychological journal should have 

 been willing to devote more than 100 pages to an article which judged by our 

 American standards does not rise above the level of theordinarv student's 'note-book.' 



