1890 SALLY 245 



was found that the number admits of being largely 

 increased by practice, until, with an exposure to view 

 of one second's duration, the estimate admits of 

 being correctly made up to between 20 and 30 objects. 

 (Preyer, ' Sitzungsber. d. Gesell. f. Med. u. Naturwiss.,' 

 1881.) In the case of the ape it is astonishing over 

 how long a time the estimate endures. Supposing, 

 for instance, that she is requested to find five coloured 

 straws. She perfectly well understands what is 

 wanted, but as coloured straws are rare in the litter, 

 she has to seek about for them, and thus it takes her 

 a long time to complete the number ; yet she remem- 

 bers how many she has successively found and put 

 into her mouth, so that when the number is com- 

 pleted she delivers it at once. After having consigned 

 them to her mouth she never looks at the straws, and 

 therefore her estimate of their number must be formed 

 either by the feeling of her mouth, or by retaining a 

 mental impression of the successive movements of her 

 arm in picking up the straws and placing them in her 

 mouth. Without being able to decide positively in 

 which of these ways she estimates the number, I am 

 inclined to think it is in the latter. But, if so, it is 

 surprising, as already remarked, over how long a time 

 this estimate by muscular sense endures. Should 

 we trust Houzeau's statement, however (and he is 

 generally trustworthy), it appears that computation 

 by muscular sense may extend in some animals over 

 a very long period. For he says that mules used in 

 the tramways at New Orleans have to make five 

 journeys from one end of the route to the other before 

 they are released, and that they make four of these 



