ANIMAL ARITHMETIC. 261 



knowledge tliat it liad to turn the spit on Saturday, or the day 

 before its master went to church. 



If this period of the seven days of the week does not exceed 

 the intelligence of a dog, the dog should be able easily to meas- 

 ure periods of two or three days. Houzeau says that he tried for 

 three consecutive weeks to repeat the same walk with his dogs, 

 every two days at exactly the same hour. It would have been 

 enough for them to count two to determine the period. On the 

 twentieth day, or the tenth periodical repetition of the excursion, 

 although the dogs enjoyed the excursion exceedingly, he never 

 remarked that they anticipated it spontaneously, or had a thought 

 of it before witnessing his preparations to go. From this, Houzeau 

 concluded that dogs could not count the days. But when actions 

 repeated daily at fixed hours were in question, the dogs knew 

 when the time came. Broderip's dog and the Santo Domingo peli- 

 can had learned, in the course of years, that the same succession 

 of events took place every Sunday. It was not, therefore, by an 

 isolated fact, but by an aggregation of facts, that they became 

 aware of the return of that day ; for not only did certain things 

 take place regularly in the family, but Sunday noises, like the 

 ringing of the bells, and unusual comings and goings, occurred 

 in the place. After continued experience, the animals acquired 

 knowledge of the succession of the events, and governed their 

 conduct accordingly. 



Houzeau also learned that some animals are capable of measur- 

 ing lapses of time that particularly interest them. He says that 

 female crocodiles abandon their eggs in the sand for ten or fifteen 

 days, according to the species, and return to the spot at the exact 

 time when they are to be hatched. It is easily conceivable that 

 animals have, in general, a more precise measure of periods which 

 concern the needs of their organic or specific life, than of the 

 more artificial periods to which they have become habituated 

 in the domesticated state or in consequence of their relations 

 with man, because an hereditary habit has always more force than 

 habits acquired by education. 



Houzeau cites facts showing that some animals can count the 

 number of similar objects or acts, provided the numbers are not 

 too high. When a magpie is watched by a company of hunters, 

 it will not move till they go away. If they go one after another, 

 it can not be deceived by one of them staying behind unless there 

 are more than four of them. Another story of similar bearing is 

 that of the tramway mules at New Orleans, which are relieved 

 and fed after making five trips. They make their trips patiently 

 and quietly till the end of the fifth, when they give evident signs 

 that they expect their usual refreshment. The horses in the coal- 

 mines of Hainault make thirty trips a day, taking their places 



