BY-PATHS OF BIOLOGY. 251 



changes and the antiquity of man, have been clearly 

 traced, thus investing geology with a new and popular 

 interest, and at the same time elucidating many of the 

 phenomena presented in the older formations. 



Now just as a surface-geology was required to com- 

 plete that science, so a surface-biology was wanted to 

 make the science of living things more complete and 

 more generally interesting, by applying the results 

 arrived at by special workers to the interpretation of 

 those external and prominent features whose endless 

 variety and beauty constitute the charm which attracts 

 us to the contemplation or to the study of nature. We 

 have the descriptive zoologist, for example, who gives us 

 the external characters of animals ; the anatomist studies 

 their internal structure ; the histologist makes known 

 the nature of their component tissues ; the embryologist 

 patiently watches the progress of their development ; the 

 systematist groups them into classes and orders, families, 

 genera, and species ; while the field-naturalist studies for 

 us their food and habits and general economy. But, till 

 quite recently, none of these earnest students nor all of 

 them combined, could answer satisfactorily, or even 

 attempted to answer, many of the simplest questions 

 concerning the external characters and general relations 

 of animals and plants. Why are flowers so wonderfully 

 varied in form and colour 1 what causes the Arctic fox 

 and the ptarmigan to turn white in winter ? why are 

 there no elephants in America and no deer in Australia ? 

 why are closely allied species rarely found together ? 

 why are male animals so frequently bright-coloured ? 

 why are extinct animals so often larger than those which 

 are now living ? what has led to the production of the 



