PROBLEMS OF DISTRIBUTION AND THEIR SOLUTION. 135 



or series of changes through which many animals pass, externally 

 to the egg, in their development. The tadpole, as every schoolboy 

 knows, grows to be a frog through successive changes converting it 

 from a fish-like organism into the type of the air-breathing terrestrial 

 adult. The caterpillar, through equally well-marked alterations of 

 form, becomes the butterfly or moth. Under the old idea of 

 zoological causation, either form undergoes metamorphosis, because, 

 to quote the words .of Kirby and Spence, "it is the will of the 

 Creator." "This, however," as Sir John Lubbock remarks, "is a 

 confession of faith, not an explanation of metamorphosis." Evolu- 

 tion satisfactorily and finally replaces the want of rational ideas of 

 metamorphosis by a higher idea of satisfactory causation, namely, 

 heredity. The frog passes in its development through a metamor- 

 phosis, because its ancestor was a fish-like organism. It repeats, as 

 an individual frog, the history of its race. So, also, an insect may 

 directly or indirectly be credited with demonstrating, by the course 

 of its development, its origin from lower stages of life. The develop- 

 ment of every animal is a brief recapitulation of the descent of its 

 species. Obscured, and often imperfect, that biography may be, 

 but nevertheless it is plainly outlined before the seeking eye and 

 understanding mind. 



If evolution has thus assisted our comprehension of why an animal 

 passes through apparently useless stages in the course of its develop- 

 ment, no less clearly has that theory brought to light the meaning 

 of the previously isolated facts of distribution. It was evolution 

 which played to these facts the part of a guardian genius ; marshalling 

 their ranks into order and arrangement, and demonstrating that 

 relationship between them which it is the province of science to 

 explain. It is necessary to dwell upon the influence which evolution 

 has exerted upon the study of distribution, simply because the latter 

 science practically dates its origin from the day when the modifica- 

 tion of existing species as a means of natural creation of new races 

 of animals and plants was recognised. And it is with the greater 

 satisfaction that one may dwell upon this mutual relationship of 

 distribution and the theory of development, since the due apprecia- 

 tion of the clear explanation which the facts of distribution receive 

 from evolution at large, constitutes a powerful counterproof of the 

 truth of that theory. It is not surprising, therefore, to find Professor 

 Huxley saying that " no truths brought to light by biological in- 

 vestigation were better calculated to inspire distrust of the dogmas 

 intruded upon science in the name of theology, than those which 

 relate to the distribution of animals and plants on the surface of 

 the earth. Very skilful accommodation was needed," continues 

 Huxley, "if the limitation of sloths to South America, and of the 

 ornithorhynchus to Australia, was to be reconciled with the literal 



