Page:Popular Science Monthly Volume 60.djvu/422

414 from 'improving' each 'shining hour.' The rest of young animals and children is quite as characteristic as their work or play. And we must be careful not to derive too much of our evidence from captive animals and restrained or metamorphosed children. We lack, too, authoritative delimitations of the periods of activity and of rest of animals. Groos, in his discussion of the play of animals, has little to say on this question other than the remark: "Of children and young animals it is true that, except when they are eating, they play all day, till at night, tired out with play, they sink to sleep." But there are night-animals, and to a certain extent, night-men, for the evening activities of the kitten, e. g., are often paralleled completely by those of her young mistress.

Of the lowest stages of animal life practically continuous activity has been asserted. Dr. Hodge and Dr. Aikins, in their study of 'The Daily Life of a Protozoan,' observe: "A Vorticella works continuously, and shows in its life no period of inactivity or rest corresponding to periods of rest in higher animals. In other words, a Vorticella never sleeps." But this is only under absolutely favorable conditions of life, for the same authors, a little further on speak of a stage of rest or encystment: "Encystment is, therefore, of the nature of an enforced 'rest,' a period of inactivity imposed by exceptional external circumstances."

As we go up the scale noticeable activity and inactivity increase in their rhythmic alternations. The fishes and lower vertebrates sleep periodically, and alternate their rest and exertion. Professor McGee characterizes the intensified activity with long intervals of inertness exemplified by the Seri Indians as 'simulating the habits of carnivorous and other lower animals.' The life history of the lion and the tiger, the elephant and the camel, the horse and the buffalo, to say nothing of other and smaller animals, furnishes us with much evidence in point. The anthropoids also, though not at all studied with reference to this theory, may afford a valuable quota of proof.

With many animals hibernation, and with many others æstivation, occupies a considerable portion of their lives, the length and broken or unbroken character of the 'sleeps' or 'rests' depending to some extent upon climate, species, individuality. How far these 'sleeps' interfere with or improve the physical and mental faculties of such animals during their season of real activity is not altogether clear, but since hibernation and æstivation must at one time have been factors in the survival of the fittest, they cannot have worked entirely to the detriment of the creatures concerned, even in later days. And the same may be said of the 'winter-sleep' of the Russian peasants.