4 GENERAL PRINCIPLES OF ZOOLOGY. 



of vital force; it has begun the attempt to explain life as the 

 summation of extremely complicated chemico-physical processes, 

 and thus to apply to the organic world those explanatory princi- 

 ples which prevail in the inorganic realm. The results obtained 

 show that it is the correct method. 



Since each organic form is the product of its development, 

 since, further, the development represents to us the summation of 

 most complicated vital processes, the explanation of the organic 

 bodily form is, therefore, in ultimate analysis a physiological 

 problem; though of course a problem whose solution lies still in 

 the indefinitely distant future. What has been actually accom- 

 plished in this direction is only the smallest beginning, even in 

 comparison with that which many falsely regard as already attained. 



Biology. According as the relations of each organism to the 

 external world are brought about through its vital phenomena, 

 there belongs to physiology, or at least is connected with it, the 

 study of the conditions of animal existence, (Ecology or Biology. 

 This branch of the science has of late attained a very considerable 

 importance. How animals are distributed over the globe, how 

 climate and conditions influence their distribution, how by known 

 factors the structure and. the mode of life become changed, are 

 questions which are to-day discussed more than ever before. 



Paleontology. Finally in the realm of zoology belongs also 

 Paleozoology or Paleontology, the study of the extinct animals. 

 For between the extinct and the living animals there exists a 

 genetic relationship : the former are the precursors of the latter, 

 and their fossil remains are the most trustworthy records of the 

 history of the race, or Phylogeny. As in human affairs the 

 present conditions can only be completely understood by the aid 

 of history, so in many cases the zoologist must draw upon the 

 results of paleontology for an explanation of the living animal 

 world. 



The science of zoology would be subdivided in the above-men- 

 tioned manner if we wished to proceed entirely on a scientific basis. 

 Yet practical considerations have made many modifications neces- 

 sary. On account of their paramount importance to the medical 

 profession human anatomy and embryology have been raised to 

 independent branches of science. In comparative physiology only 

 the most general foundations have been laid; a more special* 

 physiology exists only for man and the higher vertebrates; this, 

 too, for the above-named reasons has been made a special branch 

 of science. Paleontology also has, in addition to its specific 



