22 PRINCIPLES OF ANIMAL BIOLOGY 



really biology at all, except as the environment of one animal is made up 

 of other living things ; but it is as essential to ecology as is a knowledge of 

 physics and chemistry in general physiology. 



Somewhat related to ecology is the geographic distribution of animals, 

 or zoogeography. Ecology relates partly to local distribution of organisms, 

 as determined by environmental conditions. Zoogeography also involves 

 these questions of local distribution, since no species can live where the 

 conditions are not suitable, and wrong conditions constitute barriers to 

 distribution. However, no kind of animal is found in all the places on 

 the earth where conditions suitable for it exist. The absence of a species 

 from some regions entirely capable of supporting it is accounted for by 

 such things as the place where the group originated and the time of its 

 origin. These things are historical; ecology has nothing to do with them, 

 but they are an important part of zoogeography. The latter science is 

 therefore morphology and physiology, as far as the fitness of species to 

 occupy certain regions is concerned; and it is evolution and geolog}^ 

 whenever absence from a given region is explained by the time or place 

 of origin of the species. 



Too much emphasis should not, however, be placed upon the clearly 

 composite nature of these several biological sciences. All the divisions 

 of biology overlap to some extent; indeed, the unity of them all, which 

 makes them biology, would not exist but for such overlapping. Plants 

 share this unity with animals. There is a morphology, a physiology, a 

 taxonomy of plants. These sciences differ from the corresponding ones 

 for animals in the objects with which they deal, but not greatly in the 

 principles involved. Each of the other divisions of biology discussed 

 above relates to plants as well as to animals. It is traditional to separate 

 botany from zoology, but there is scarcely more difference between plants 

 and animals as they relate to one of these sciences than there is between 

 some of the more extreme animals. 



References 



LocY, W. A. Biology and Its Makers. Henry Holt & Company, Inc. (Especially 



Chaps. I-IV, VI, VII, XI.) 

 LocY, W. A. Growth of Biology. Henry Holt & Company, Inc. (Particularly 



Chaps. II, IV, IX, X.) 

 MiALL, L. C. The Early Naturalists, Their Lives and Work. The Macmillan 



Company. (Sec. V, minute anatomists; Sec. VIII, part on Linnaeus.) 

 NordenskiOld, E. History of Biology, .\lfred A. Knopf, Inc. (Especially Chaps. 



I, II, V, VII, VIII, XIV of Part 1. ^Fhe rest of the book will be better appre- 

 ciated after several advanced courses in biology.) 

 OsBOHN, H. F. From the Greeks to Darwin. The Macniilian Company. (Hi.story 



of the evolution idea over the period indicated.) ^ 



Singer, C. Biology: History. Medicine, History of. Articles in Encyclopaedia 



Britannica. 



