10 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



tion of continents, and to discover the highways of distribution and 

 the causes of migration in past epochs." 6 This was particularly true in 

 the half century following Darwin's Origin of Species, when the study 

 of homologies overshadowed all other lines of research in zoology. 

 During that period, historic zoogeography was enthroned, was actively 

 investigated, and now exhibits in consequence a fine series of well- 

 established and connected results. On the other hand it must be 

 admitted that more sins were committed in this division of zoogeog- 

 raphy than in any other through the proposal of unwarranted and 

 frivolous hypotheses. The data are often meager, geological evidence 

 wanting, and the sources of error great. No uniformity of opinion has 

 been reached in even the most fundamental problems, such as that of 

 the permanence or transitory nature of continents and oceans. 



In contrast with this situation in historical zoogeography, ecologi- 

 cal zoogeography bears the germs of a truly causal science. Although 

 it is still in its infancy, some general laws have already been estab- 

 lished, such as the application of the law of minima to the phenomena 

 of distribution (cf. p. 21), Bergmann's Rule (Chapter XX), and the 

 correlation between the weight of the heart and the isotherms of 

 climate. Further active research will produce a blossoming of this 

 science like that of its elder sister, ecological phytogeography, in the 

 past generation. 



BIBLIOGRAPHY 



1) Engell, 1911, Petermanns Mitt., Erganz., 171, p. 2 ft.— 2) Hartert, 1910, 

 Die Vogel der palaarktischen Fauna, 1, p. IV-VI; Reichenow, 1901, Verh. 5. Int. 

 Orn. Cgr., Berlin, p. 910-914; Rensch, 1934, Kurze Anweisung fur zoologisch-sys- 

 tematische Studien. — 3) Sarasin & Sarasin, 1901, Materialien zur Naturge- 

 schichte der Insel Celebes, 3.-4) Handlirsch, 1913, SB. Akad. Wiss. Wien (m.- 

 n. Kl.), 122, Abt. 1, p. 116.— 5) Burckhardt, 1902, Zool. Jb., Syst., 15, p. 499-536. 

 — 6) Sarasin & Sarasin, 1898, op. cit., 1, p. V. 



