Karl groos divides the play of animals into the following types :

Experimental Play. This includes all play which enables the animal to get control of its muscles, and involves stretching, straining the limbs, pulling, clawing, etc.

Puppies very early begin to gnaw any object, and a kitten, to play with its tail ; and all animals of the cat tribe have been observed at an early age to play with the mother’s tail.

Movement Play. Play involving change of place for its own sake. One of the best examples of this is the delight birds take in swinging. Many birds seem to choose the highest branches of a tree in order to give vent to their love of this pastime. Romanes speaks with great assurance of the movement play of fishes, but the fact that play of this kind is found so low down in the animal world still needs confirmation.

Hunting Plays. This type of play Groos divides into two classes :

Hunting with live prey.

Hunting a lifeless object.

Many animals of the same species chase each other with great excitement and the cat’s love of torturing its victim is probably a form of this kind of play. The joy with which dogs run after a ball or stone and the fact that a dog will often play with an object alone, are examples of play which involve the chasing instinct.

Fighting Plays. The love of teasing, hustling and mock fighting appears to be an attitude of all young male animals, and in many cases the same characteristic develops in the female. The fact that dogs go through all the appearance of real conflict without hurting each other is well known.

Constructive Arts. The most interesting example of this is that of the bower bird who builds a hall or antechamber to his nest which he decorates with the brightest colours, and which is used entirely for the purposes of courtship. Both sexes take part in its construction but the male is the director.

Nursery Plays. Under this heading Groos quotes many cases of animals which adopt the young of their own or other species and also refers to the quaint friendships often observed among animals. It is doubtful whether either of these characteristics can really be classed under “Play.”

Sex Plays. By far the greater number of the plays of animals come under the heading of Love Plays which are connected with powerful instincts of sex. These include the many playful accompaniments of courtship either by means of display or song. It is interesting to note that amongst the higher animals many sex plays are taken part in by the young before they reach the stage in which the true instinct appears. Groos regards this phenomenon as a proof of the Practice Theory of Play.