4 LEISURE-TIME STUDIES. 



the science of functions ; and its study includes the con- 

 sideration of the many processes whereby the organism 

 nourishes itself, reproduces its species, and through its ner- 

 vous system maintains relations with and reacts upon its 

 surroundings. The three great functions of Nutrition, Re- 

 production, and Inncrvation, thus fall to be considered under 

 the head of Physiology. The third department of biological 

 science is that of Distribution. We now regard the living 

 being in its relations to its environments, past and present. 

 The study of Geographical Distribution, or that in space, 

 leads us to note its habitat in the existing world ; whilst 

 Geological Distribution, or that in time, elucidates for us 

 the conditions under which it existed in past periods of the 

 earth's history, and seeks to make us acquainted with the 

 relations of living beings to their surroundings in epochs 

 anterior to our own day. A fourth department of biological 

 inquiry, which in one sense may be said to unite the interests 

 of the preceding branches, is that to which the name of 

 ^Etiology has been given. Through this latter department, 

 which may be viewed as the result of the promulgation of 

 the modern theories of Evolution and Descent, we inves- 

 tigate, as far as is possible, by the light of hypothesis and 

 development, the probable derivation of living beings ; and 

 we thus seek to unite by a thread of continuity the various 

 and diverse relationships so clearly to be discerned in either 

 kingdom of living nature. Such a work assists us in framing 

 a feasible plan of classification, based upon the develop- 

 ment of living forms, and presents a highly attractive field 

 for investigation. 



Having thus noted the essential features comprised in 

 the modern study of living beings, we may next look at the 

 wider and incidental relations which the study of Biology 

 may be shown to possess to other branches of inquiry. The 

 work of the biologist cannot be carried on in a successful 

 and satisfactory manner without aid from many other, and, 

 in many cases, apparently dissociated sciences. The in- 

 quiry into the most common phenomena of animal and 



