BEHAVIOR OF VERTEBRATES 457 



eighth of the total work was performed, whereas, during the 

 first thirty per cent, of the life span, three-eighths of the total 

 work was done. 



Unexercised animals (controls) reached their maximum weight 

 at an early period. At corresponding ages the controls had a 

 greater absolute weight than the exercised rats. The unexer- 

 cised animals lived longer than the exercised ones. 



Slonaker's conclusions probably hav*e not the universality he 

 claims for them. In the first place, the activity necessary to 

 . cause the cage to revolve cannot be taken as an index of all 

 other forms of activity. Probably many other forms of activity 

 have a far different type of life history than that involved in 

 causing the cage to revolve. Further, Slonaker's woik tells us 

 really nothing of the relative amounts of work the animals can 

 do at different ages. This phase of the subject is not touched 

 upon by him. He sets the adult rat to revolving a mechanism 

 so delicate that a twenty-eight days old animal can work it. 

 His records show not the amount of work the animal can do 

 at different ages, nor even the relative lengths of time during 

 which this activity would take place under slightly different 

 conditions. In other words, Slonaker is dealing rathei with the 

 tempoial aspects of a certain type of activity. Often the dis- 

 tribution of time in running is misleading, too, because of the 

 unequal effort called forth between young and old. The rat 

 at twenty-eight days is probably working up very near to his 

 maximum limit of effort in causing the cage to turn; he may 

 leave off at any time by reason of exhaustion; whereas the 

 adult rat may cease activity at the end of two hours merely 

 because a stronger stimulus impels him elsewhere. It seems to 

 the reviewer to be hard to draw any legitimate conclusion from 

 Slonaker's work until there can be some suitable method of 

 getting a measure of fatigue, etc. 



Coburn (3) records some specimens of the house mouse (Miis 

 musculus) which were able to sing in the sense in which that 

 act has been described by Lee and Brehm. The "singing" re- 

 sembles the soft chirp of a bird; it is best described as a rapid, 

 whole toned trill involving the tones of c and d. The clang 

 character is similar to that of flute or pipe tones. 



Cole (4) summarizes his observations on the instincts of rac- 

 coons and their use of the senses. He gives the following as 



