DESIGN IN NATURE 



PLATE LII 



exhiliit five digits, and the posterior extremities five toes, ^vith swimming membranes between, The seal swinis almost exclusi y y 

 means of its expanded, webbed, hind extremities or flippers, which it lashes vigorously from side to side as a fish does its tail. '-"^'^ . 

 flippers open and close during the effective and iion-eft'ective strokes, and confer on the trunk m swimming a slight degree oi loba . 

 The anterior extremities or flippers are employed chiefly in balancing and turning, and m seeking the surface ot tne waier lu 

 breathing purposes. 



Fig. 3.— The manatee or sea-cow (Maivitus americamm). Drawn from a fresh specimen by C. Berjeau. The anterior extremities 

 or flippers alone persist ; the posterior ones being replaced by a broadly expanded tail. The tail resembles that of the ftsn, Dui m 

 swimming it is made to vibrate from above downwards or vertically, instead of laterally. This arrangement enables tne a"'""^ 

 to reach the surface of the water quickly for breathing purposes and to disappear suddenly if m danger. The anterior extremuies or 

 flippers assist in these movements and in turning. The manatee is more fish-like in appearance than either the seat or sea-ueai. 

 Design and adaptation can alone account for the shape and movements of the manatee. 



Fro. 4.— The porpoise (Phocsena eommums). Drawn from a fresh specimen by C. Berjeau. This sea mammal altogether resembles 

 a fish in general appearance. The anterior flippers can no longer be recognised as arms. They are so dimmished in size and so a terea 

 in shape as to resemble the pectoral fins of fishes. In like manner the posterior flippers are supplanted by a delicately-outlinecl, 

 powerful swimming tail. The porpoise is one of the best swimmers known. The tail is made to vibrate vertically, and makes 

 figure-of-8 movements. The same is true of the manatee, though to a less extent. In both cases the tail m swimming twists and 

 untwists after the manner of a screw. The swimming adaptations observable in the sea-bear, seal, and manatee culminate in the 

 porpoise. Design has produced a perfect swimming form. 



Fig. 5.— The salmon trout (Salmo trtitta). Drawn from a fresh specimen by C. Berjeau. This maybe taken as a typical fish. 

 It has pectoral, dorsal, ventral, and anal fins, and a finely-formed tail. The fins and tail are carefully-graduated structures, and supply 

 good examples of longitudinal and radiating cleavage. Tlie body is specially designed to diminish resistance when it is forced through 

 the water and the tail and lower third of the body combined form a powerful propeller. The stroke is delivered laterally, and the 

 movements made bv the tail are figure-of-8, slightly rotatory screw movements. In the fish, the anterior and posterior extremities may 

 be said to have entirely disappeared, their places being taken by the pectoral and ventral fins. The fins m fishes assist m balancing 

 and turning, but, in the majority of cases, take little or no part in propulsion. 



Pig. 6 —The flying-fish {Exoccetus robustus). Drawn from a recent specimen by C. Berjeau. The flying-fish forms a connecting 

 link between the water and the air : it swims well, and takes considerable flights. It is very amply supplied with fins. The pectoral 

 fins are as large relatively to the size and weight of the body as the wings of many insects and birds. They are true wings as regards 

 shape and structure. They and the other fins furnish a striking example of longitudinal and radiating cleavage. The flying-fish 

 conclusively proves that in order both to swim and fly special arrangements must be made ; what are virtually true wings must be added 

 to the swimming tail. Here again design and adaptation come in. Neither the wings or tail are chance products. Similar remarks 

 apply to all organs of locomotion, liowever fashioned and however applied. They are in every case specially designed structures. 



Fig. 7.— The little auk (Aptenodytes minor, Linn.). Drawn from living specimen by C. Berjeau. In this bird the flying wings 

 are dwarfed and employed as swimming and diving organs, with or without the feet. They are triangular in shape and graduated like 

 other wings, their small size and want of feathers rendering them useless for flying in the air. They are flexible and elastic, but 

 stiffer than ordinary wings ; a modification necessitated by the greater density of water as compared with air. They are made to 

 vibrate like other wings and twist and untwist during their action and make figure-of-8 screw movements. The flight of the bird 

 under water is astonishingly rapid and graceful, as the Author can testify from careful observation. The modified wings of the little 

 auk furnish another example of design. 



Fig. 8. — The triton {Triton oristalus). Drawn from the life by C. Berjeau. This curious creature is adapted for land and 

 water transit, and is accordingly furnished with travelling extremities and a large, powerful, swimming tail. Similar arrangements 

 obtain in the crocodile. The triton connects the land and water as the flying-fish connects the water and the air in the matter of 

 transit. In both cases special modifications are required in the locomotory organs. The means and the ends are alike proofs of 

 design. 



PLATE LIII 



Plate liii. illustrates the variety in shape and increase in size of the travelling organs required for land, water, 

 and air transit respectively : how fishes in svnmming, birds in flying, and quadrupeds and bipeds in walking, make 

 double or figure-of-8 curves as explained by the Author in 1867, 1868, and 1870.^ 



Fig. 1. — Shows the extreme modifications in the travelling organs required for land, water, and air. 



A. Chillingham bull {Bos scoticus). Reveals ponderous body and the small extremities and feet adapted for land transit ; t, ii, 

 indicate the double curves made by the two anterior extremities, and r, s, those made by the posterior extremities in walking. As the 

 right fore and left hind legs move together to form one step, and the left fore and right hind legs move together to form a second step, 

 the double curves form a Hgnre-of-8. 



B. The hawk's-bill turtle {Eretmodtelys imbriaUa). Displays large modified anterior and posterior extremities, adapted for 

 water transit. Both the anterior and posterior extremities, especially the former, are constructed on the wing model, being triangular 

 in shape, and thick and semi-rigid at the roots and along the anterior margins, and thin and elastic at the tips and along the posterior 

 margins. They act as wings in swimming. The travelling organs of the turtle are relatively much larger than those of the Chillingham 

 bull(A>. 



C. The bat {Phyllorhina gracilis, Peters). This anomalous and (.[uaint creature exhibits a still greater degree of modificntion in the 

 anterior and posterior extremities to meet the exigencies of aerial transit. Here the body is dwarfed and the anterior extremities 

 enormously enlarged to produce the necessary framework to support, in conjunction with the posterior extremities and tail, the widely 

 expanded wings. It would be difficult to adduce more perfect examples of design than are furnished by A, B, and C, respectively. 



Fl 



1 "On the Various Modes of Flight in Relation to Aeronautics" {Pmc. Soy. Inst. Ot. Britain) ; " On the Mechanical Appliances by which 

 iglit is Attained in tlie Animal Kingdom " (Tmns. Linn. Sac, vol. xxvi ) ; " On the Physiology of Wings " (Trans, Rini. Soc. Eitin,, vol. xxvi.). 



