102 



ANIMAL LOCOMOTION. 



feet — the tail becoming larger, and the extremities (anterior) 

 diminishing, in the manatee (fig. 34, p. 73) and porpoise (fig. 

 33, p. 73), until we arrive at the fish (fig. 30, p. 65), where 

 not only the tail but the lower half of the body is actively 

 engaged in natation. Turning from the water to the air, we 

 observe a remarkable modification in the huge pectoral fins 

 of the flying-fish (fig. 51, p. 98), these enabling the creature 

 to take enormous leaps, and serving as pseudo-pinions. Turn- 

 ing in like manner from the earth to the air, we encounter 

 the immense tegumentary expansions of the flying-dragon 

 (fig. 15, p. 35) and galeopithecus (fig. 16, p. 35), the floating 

 or buoying area of which greatly exceeds that of some of the 

 flying beetles. 



In those animals which fly, as bats (fig. 17, p. 36), insects 

 (figs. 57 and 58, p. 124 and 125), and birds (figs. 59 and 60, 

 p. 126), the travelling surfaces, because of the extreme tenuity 

 of the air, are prodigiously augmented ; these in many instances 

 greatly exceeding the actual area of the body. While, therefore, 

 the movements involved in walking, swimming, and flying are 

 to be traced in the first instance to the shortening and lengtli- 

 ening of the muscular, elastic, and other tissues operating on 

 the bones, and their peculiar articular surfaces; they are to 

 be referred in the second instance to the extent and configu- 

 ration of the travelling areas — these on all occasions being 

 accurately adapted to the capacity and strength of the animal 

 and the density of the medium on or in which it is intended 

 to progress. Thus the land supplies the resistance, and 

 afl*ords the support necessary to prevent the small feet of 

 land animals from sinking to dangerous depths, while the 

 water, immensely less resisting, furnishes the peculiar medium 

 requisite for buoying the fish, and for exposing, without 

 danger and to most advantage, the large surface contained 

 in its ponderous lashing tail, — the air, unseen and unfelt, 

 furnishing that quickly yielding and subtle element in which 

 the greatly expanded pinions of the insect, bat, and bird are 

 made to vibrate with lightning rapidity, discoursing, as they 

 do so, a soft and stirring music very delightful to the lovei 

 of nature. 



