130 STUDIES IN LIFE AND SENSE. 



itself to its environments which gives to the living body its chief 

 characteristics. It is the action and reaction of the organism upon 

 the world around it, and its adaptation to its surroundings, which 

 impart to the animal or plant its plainest differences from the 

 inorganic things around. Hence we distinguish a third function of 

 the living being ; that of innervation or relation. Exercised through 

 the medium of a nervous system or its representative tissues, this 

 function of relation regulates and controls, whilst it connects and 

 harmonises, the other actions of which life's activities consist. The 

 animal or plant, regarded from a physiological standpoint, lives thus 

 a threefold existence, and performs a triple round of duties. It 

 nourishes itself, it reproduces its race, and it develops and exhibits 

 relations with its surroundings. The knowledge which demonstrates 

 how these functions are performed answers the second of our four 

 questions " How does it live ? " 



Structure and functions, all-important as their detail may be for 

 the understanding of animal and plant histories, do not, however, 

 constitute or bound the entire range of biological observation. The 

 inquiries of even the childish stage of man's culture concerning the 

 living as well as the non-living universe, include, above all other 

 points, the inquiry, " Where is it found ? " Especially natural does 

 such a question appear when applied to the living tenants of the 

 globe. When we ask ourselves where any organism is found, in 

 what quarter of the globe it is plentiful, where it is scarce, or where, 

 lastly, it is never to be discovered, we are in reality approaching 

 topics which lead us tolerably near to the ultimate questions of all 

 biological study. It is the science of distribution which professes 

 to answer the questions relating to the whereabouts of animals and 

 plants in the world as it now exists, and in anterior epochs of our 

 globe as well. Distribution thus includes two most natural divisions 

 or lines of inquiry. It summarises the existing life of the globe in its 

 inquiries regarding the geography of living things, or their distribu- 

 tion in space, as it is technically termed ; whilst it no less succinctly 

 attempts the solution of the problems relating to the past history of 

 animals and plants, when, proceeding to avail itself of the informa- 

 tion collected by geology, it pictures for us their distribution in time. 



The knowledge of the structure, functions, and distribution of a 

 living being once comprehended all that science could hope to know 

 of its history. Contenting itself with the fact that living beings are, 

 biology might regard the knowledge which these three queries, 

 "what," "how," and "where," supplied, as all-sufficient for the 

 furthest mental demands. But the newer epoch of biology includes 

 a fourth question in its list of queries concerning living things. It 

 presents for solution yet another problem, in the terms of which is 

 focussed all the knowledge gained in other departments of biological 



