Adaptation 

 Adaptations 



SCIENTIFIC SIDE-LIGHTS 



12 



semble so closely the living urchins of the 

 abyss. HICKSON Fauna of the Deep Sea, 

 ch. 5, p. 102. (A., 1894.) 



57. 



Dogs Change during 



Growth Heredity of Acquired Characters. 

 The influence of physical conditions in 

 modifying the constitution is well known to 

 be most strongly exerted during the earlier 

 period of life; for as long as the organism 

 is in process of development it will grow 

 to its environment, as it Avill not do at a 

 later epoch, when it will either resist or 

 succumb. We are told by Sir Charles Lyell 

 that the Cornish miners, who went out some 

 sixty years ago to work the Real del Monte 

 mines in Mexico, took out some greyhounds 

 to hunt the hares Avhich abound on the ele- 

 vated plateaux of that country; but that, 

 in consequence of the rarefied condition of 

 the air, the dogs could not continue the 

 chase, but lay down panting for breath. 

 The offspring of those dogs, however, 

 brought up at this elevation, were able to 

 run down the hares as well as if both had 

 been on a lower level. The constitution of 

 the young dogs adapted itself to the envi- 

 ronment in which they grew up ; but whence 

 that adaptability? We do not find it in 

 any but living organisms; no physical prop- 

 erty gives the least account of it. CARPEN- 

 TER Nature and Man, lect. 15, p. 440. (A., 

 1889.) 



58. 



Kangaroo Must 

 ivhile Its Fore- 



Traverse Desert Swiftly, 

 feet Serve as Hands. Some of them [kan- 

 garoos] are very large animals, as bulky as 

 deer, and rapidity of locomotion is espe- 

 cially necessary for a large animal which in- 

 habits a country subject to such severe and 

 widely extended droughts as is Australia. 

 . . . In the kangaroos we have animals 

 which require to use their front limbs for 

 purposes of more or less delicate manipula- 

 tion, with respect to the economy of the 

 " pouch." Accordingly, for such creatures 

 to be able to inhabit such a country, the 

 hind limbs must by themselves answer the 

 purpose of both the front and hind limbs of 

 deer and antelopes. But the kangaroo's 

 limbs are quite admirably suited to its 

 needs. The front pair serve as prehensile 

 manipulating organs, while the hind pair 

 amply suffice to carry the animal over great 

 distances and rapidly traverse wide, arid 

 plains in pursuit of rare and distant water. 

 MIVART Types of Animal Life, ch. 2, p. 

 48. (L. B. & Co., 1893.) 



59. Lizards That Live 



inithout Water. The individuals [lizards 

 of the terrestrial species of Amblyrhyncus, 

 of the Galapagos Islands], and they are the 

 greater number, which inhabit the lower 

 country, can scarcely taste a drop of water 

 throughout the year; but they consume 

 much of the succulent cactus, the branches 

 of which are occasionallv broken off by the 

 wind. I several times threw a piece to two 



or three of them when together ; and it was 

 amusing enough to see them trying to seize 

 and carry it away in their mouths, like so 

 many hungry dogs with a bone. DARWIN 

 Naturalist's Voyage Around the World, ch. 

 17, p. 389. (A., 1893.) 



60. 



The Sloth, as Known 



to Recent Science. Far from being an " im- 

 perfect sketch " of animal life, it [the 

 sloth] is a fully completed study of perfect 

 adaptation of structure to need. The sloth 

 is an animal specially formed to dwell no- 

 where but in luxuriant forests. But to live 

 thus . . . necessitates a special and 

 peculiar structure. ... It is impos- 

 sible that an animal formed to do this can 

 at the same time be organized so as to move 

 well and freely on the surface of the ground, 

 for which the stress and leverage must be 

 altogether different. Hence the structure of 

 such a creature must seem very defective to 

 any one who only observes its motions on 

 the surface of the soil, a position in which 

 it naturally hardly if ever finds itself. 

 . . . Sloths pass their lives hanging 

 under the branches of trees, back down- 

 wards, and so they can sleep securely. The 

 fingers and toes of each hand and foot are 

 so closely bound together that they cannot 

 be separated; while each finger and toe is 

 furnished with an enormously long and very 

 strong nail, greatly curved. W'hen at rest 

 the hands and feet are so bent that each 

 thus forms a strong hook, and it requires an 

 effort on the part of the animal to unhook 

 either a hand or foot from the branch it 

 clasps. Thus it is that the sloth can sleep 

 suspended from a branch, and remain so 

 after death. MIVART Types of Animal Life, 

 ch. 9, p. 249. (L. B. &Co., 1893.) 



01. 



Vast Size of Whale 



Possible Only for Marine Animal. There 

 results a limitation of growth in a land- 

 animal, which does not exist for an animal 

 living in the water. If, after observing the 

 swaying flesh of an elephant as it walks 

 along, we consider what would happen could 

 there be formed a land-animal equal in mass 

 to the whale, it needs no argument to show 

 that such a creature could not stand, much 

 less move about. But in the water the 

 strain put upon its structures by the 

 weights of its various parts is almost if not 

 quite taken away. SPENCER Biology, pt. 

 ii, ch. 1, p. 156. (A., 1900.) 



62. ADAPTATION TO ENVIRONMENT 



BY MEN Arboreal Human Life Former 

 South American Tree-dwellers. This re- 

 gion [South American steppes], which may 

 be regarded as peculiarly the habitation of 

 wild animals, would not have been chosen as 

 a place of settlement by nomadic hordes, 

 who prefer a vegetable diet, had it not pos- 

 sessed some few fan-palms (Mauritia) scat- 

 tered here and there. The beneficent quali- 

 ties of this tree of life have been univer- 

 sally celebrated. Upon this alone subsist 



