2 THOMAS WILLIAM BROCKBANK 



loss at 120 days and 140 days, respectively, for the Cowbird 

 and the Pigeon. Among other conclusions Rouse (6) men- 

 tions that the Pigeon retains fairly well for 6 weeks. The 

 period of retention on a simple labyrinth is given by 

 Hunter (11) as 28 days for the Pigeon.. Cole states (7) 

 that the memory for a combination of 7 fastenings was far 

 from perfect in the Raccoon at the end of approximately 

 5 months. With the same animal Davis (8) found that 

 retention for simple fastenings was very good at the end 

 of one year and even longer. Colvin and Burford tested 

 memory in a dog and a squirrel on color discrimination. 

 The dog exhibited no loss of discrimination for the standard 

 color at the end of 3 weeks; after 2 months the squirrel 

 showed no evidence of discrimination for the color, " red- 

 red-orange." In reference to the dog, Johnson (16) notes 

 that, after 60 days, loss in accuracy was only about 10 per 

 cent in the retention of habits of manipulation. Thorndike 

 observed (10) that chicks are practically perfect on a simple 

 labyrinth after 20 days. Breed (14) made a further ad- 

 vance on the conclusions of Thorndike and found that 30 

 days was the approximate periods for retention in the 

 chick. He states further that the chick which learns most 

 rapidly retains the best. Casteel (13) shows that the 

 Painted Turtle retains a simple sensory habit without loss 

 for 2 weeks. In his work on the Canadian Porcupine, 

 Sackett (15) shows that it retained the Hampton Court 

 maze for 10 days with some loss. Basset (17) and Ulrich 

 (18) have found that after a 60-day period most rats did 

 not retain the maze perfectly. Further experimental con- 

 clusions by Ulrich seem to indicate that the effect of the 

 distribution of effort in learning is maintained in reten- 

 tion within certain undefined limits; but his results on 

 this point are inconclusive. Hubbert (21) tested rats 

 90 days on the Round Maze, but established nothing 

 definite. 



The foregoing summary of experiments on retention in 

 animals clearly shows that the little already done on the 

 subject lacks systematic study and a definite statement 

 of results however brief. Those methods which employ 

 only an increase or decrease of time or speed, and also 



