53° 



THE POPULAR SCIENCE MONTHLY. 



used as fins only. " Every variety of motion peculiar to land, air, and 

 water-navigating animals, as such, is imitated by others which take to 

 the elements in question, secondarily or at intervals." It is probably 

 true, however, that no animal which lives indiscriminately in two me- 

 dia attains the highest development for traveling in or upon either. 

 In such cases the maximum speed is not attained. Those animals, 

 says the author, which swim the best, walk, as a rule, with difficulty, 

 and vice versa, as the movements of the auk and the seal, in and out 

 of water, amply testify. It is evident that all the supposed gaps be- 

 tween typical forms for locomotion are bridged by forms intermediate, 

 and the author's position is fully sustained, that walking, swimming, 

 and flying, are essentially the same. 



Fig. 2. 



The Little Penguin, adapted exclusively for swimming and diving. In this quaint bird the 

 wing forms a perfect screw, and is employed as such in swimming and diving. 



Before entering upon the question of the movement and functions 

 of specialized organs for locomotion, attention is invited to the inter- 

 esting statement that, however wonderful and beautiful, in its way, 

 the bony skeleton may be, it is after all only an adjunct to locomotion, 

 and of motion in general — that all the really essential movements of 

 ah animal occur in the soft parts. " The osseous system is therefore to 

 be regarded as secondary in importance to the muscular, of which it 

 may be considered a differentiation. Instead of regarding the muscles 

 as adapted to the bones, the bones ought to be regarded as adapted 

 to the muscles. Bones have no power either of originating or perpet- 

 uating motion. This begins and terminates in the muscles." 



The bones are the passive organs of locomotion, in the movement 

 of which muscular force is expended. In land animals, as a rule, the 

 bones are harder and more elastic than in aquatic species. The carti- 

 laginous and spongy bones of many fishes would be ill suited to bear 

 the strains and shocks of terrestrial progression. 



The velocity with which a limb may be moved will depend upon 

 tho acuteness of the angles of its several bones. Hence the fleetness 

 of many animals, in which the angles formed by the bones are acute. 

 This is well shown in the skeleton of a deer, of which Fig. 3 is an ex- 



