258 The Unity of the Organism 



direct way possibly with feeding or reproduction or migra- 

 tion or some other vital function — the question still remains, 

 why so much of it? And to this no probable or even ra- 

 tional answer is forthcoming from the standpoint of adapta- 

 tion and utility, taking these terms in their usual meaning. 



Here is another case from the mammalia, the possible 

 adaptive significance of which is still more remote, if any- 

 thing, than that of the behavior of the whale. Many indi- 

 vidual mice of the genus Peromyscus being used by Doctor 

 Sumner and Mr. Collins in their researches on heredity and 

 environmental influence at the Scripps Institution take to 

 throwing back summersaults in their cages. The more com- 

 mon performance consists in a run along the floor of the 

 wooden cage and up its side to near the top, then a quick, 

 strong jump backward clear across the cage, the feet being 

 uppermost during the first part of the leap but coming to 

 rights again by the time the landing is made. Here again 

 the question of why the mice do this seemingly useless thing 

 is not so interesting for the present discussion as that of 

 why they do it so much. 



The high flight of some species of birds, the great eleva- 

 tions being reached by long, regular upward spirals, would 

 appear to come under the head of non-adaptive, superfluous 

 action. The sand-hill crane, Grus Tuexicana, may be taken 

 as an instance of a bird given to this habit. Surely such 

 flights by this species can have nothing to do with food- 

 getting, since in the excursions the bird is going directly 

 away from, instead of into, the region where its ^ food 

 abounds. It eats snakes, frogs and other creeping animals, 

 and various seeds and roots. Nor is there any evidence that 

 the flights are concerned with the mating function, nor yet 

 with migration, though one might possibly imagine that 

 while on the excursions the birds learn, after a fashion, the 

 topography of the surrounding regions. 



The high-diving and booming of the night-hawk, Cordeiles 



