The play of animals and children may be classified roughly in two main groups : play based on experimentation ; and more or less organized play. The baby who continually throws his spoon on the floor, the kitten flying round after its own tail, are well-known examples of the first type of play, which owes its attraction to the continued use of similar and allied muscles. This form of play is the one usually found amongst animals, while the more or less organized play is prominent amongst all but very young children. Romanes, 1 however, quotes examples of apparently organized play amongst ants, and this statement has recently been confirmed by Step, while Groos, in his exhaustive study of the play of animals, gives many instances of such amongst birds and the higher vertebrates.