90 



ANIMAL LOCOMOTION. 



The same remarks apply to the movements of the extremi- 

 ties of the triton (fig. 45, p. 89) and crocodile, when swimming, 

 and to the feebly developed corresponding members in the 

 lepidosiren, proteus, and axolotl, specimens of all of which are 

 to be seen in the Zoological Society's Gardens, London. 

 In the latter, natation is effected principally, if not altogether, 

 by the tail and lower half of the body, which is largely de- 

 veloped and flattened laterally for this purpose, as in the fish. 



The muscular power exercised by the fishes, the cetaceans, 

 and the seals in swimming, is conserved to a remarkable 

 extent by the momentum which the body rapidly acquires — 

 the velocity attained by the mass diminishing the degree of 

 exertion required in the individual or integral parts. This 

 holds true of all animals, whether they move on the land or 

 on or in the water or air. 



The animals which furnish the connecting link between 

 the water and the air are the diving-birds on the one hand, 

 and the flying-fishes on the other, — the former using their 

 wings for flying above and through the water, as occasion 

 demands ; the latter sustaining themselves for considerable 

 intervals in the air by means of their enormous pectoral fins. 



Flight under water, etc. — Mr. Macgillivray thus describes a 

 flock of red mergansers which he observed pursuing sand-eels 

 in one of the shallow sandy bays of the Outer Hebrides : — 

 " The birds seemed to move under the water with almost as 

 much velocity as in the air, and often rose to breathe at a 

 distance of 200 yards from the spot ' at which they had 

 dived."! 



In birds which fly indiscriminately above and beneath the 

 water, the wing is provided with stiff leathers, and reduced 

 to a minimum as regards size. In subaqueous flight the 

 wings may act by themselves, as in the guillemots, or in con- 

 junction with the feet, as in the grebes.^ To convert the 



1 History of British Birds, vol. i. p. 48. 



2 The guillemots in diving do not use their feet ; so that they literally fly 

 under the water. Their wings for this purpose are reduced to the smallest 

 possible dimensions consistent with flight. The loons, on the other hand, 

 while they employ their feet, rarely, if ever, use their wings. The sub- 

 aqueous progression of the grebe resembles that of the rog. — Cuvier's Animal 

 Kingdom, Lond. 1840, pp. 252, 253. 



