it was pushed back he fell into a rage.  His inference that the nail-head could not be pulled through was entirely correct; he had failed to foresee that it could be pushed back.  Many such instances have probably come within the range of your observation, if you have noticed them.  But many of the facts which Mr. Romanes gives us concerning the intelligence of monkeys, apes, and baboons would not disgrace the intelligence of children or men.

Mr. Romanes relates the following account of a little capuchin monkey from Brazil: 

“To-day he obtained possession of a hearth-brush, one of the kind which has the handle screwed into the brush.  He soon found the way to unscrew the handle, and having done that he immediately began to try to find out the way to screw it in again.  This he in time accomplished.  At first he put the wrong end of the handle into the hole, but turned it round and round the right way for screwing.  Finding it did not hold he turned the other end of the handle and carefully stuck it into the hole, and began again to turn it the right way.  It was of course a difficult feat for him to perform, for he required both his hands in order to screw it in, and the long bristles of the brush prevented it from remaining steady or with the right side up.  He held the brush with his hind hand, but even so it was very difficult for him to get the first turn of the screw to fit into the thread; he worked at it, however, with the most unwearying perseverance until he got the first turn of the screw to catch, and he then quickly turned it round and round until it was screwed up to the end.  The most remarkable thing was, that however often he was disappointed in the beginning, he never was induced to try turning the handle the wrong way; he always screwed it from right to left.  As soon as he had accomplished his wish he unscrewed it again, and then screwed it in again the second time rather more easily than the first, and so on many times.  When he had become by practice tolerably perfect in screwing and unscrewing, he gave it up and took to some other amusement.  One remarkable thing is that he should take so much trouble to do that which is no material benefit to him.  The desire to accomplish a chosen task seems a sufficient inducement to lead him to take any amount of trouble.  This seems a very human feeling, such as is not shown, I believe, by any other animal.  It is not the desire of praise, as he never notices people looking on; it is simply the desire to achieve an object for the sake of achieving an object, and he never rests nor allows his attention to be distracted until it is done....

“As my sister once observed while we were watching him conducting some of his researches, in oblivion to his food and all his other surroundings—­’When a monkey behaves like this it is no wonder that man is a scientific animal!’"[A]

  [Footnote A:  Romanes:  Animal Intelligence, pp. 490, 498.]