ZOOLOGICAL SCIENCES 5 



Broadly speaking, the environment consists of the entire universe 

 outside the animal's body, and a great deal that may be internal, 

 such as chemical substances circulating in the blood, or the body 

 heat of a higher animal. Narrowly speaking, it comprises the 

 more immediate surroundings; but factors remote in their origin, 

 such as the sun's light and heat, and even the light of the moon, 

 may be important. In recent years the study of organisms 

 in relation to their environment has come to be designated Ecology. 

 To study animals as thus related to their surroundings, it is neces- 

 sary to classify them. Hence, Taxonomy, or the science of classi- 

 fication, is related to Ecology, as the table shows. Zoogeography, 

 or the distribution of animals over the surface of the earth, is 

 likewise important; and one might include the distribution 

 of organisms in geologic time as shown by the study of Paleontol- 

 ogy. Since functions are everywhere important in relation to 

 environment, Physiology is also concerned, and with it Morphology 

 and Pathology, for the reasons indicated in a preceding paragraph. 



Classification. — The problem of arranging the various kinds of 

 animals in some orderly manner must have presented itself ever 

 to primitive peoples. The " beasts of the earth," the " fowls oi 

 the air," the " fish of the sea," and " everything that creepeth," 

 represents an early attempt of this nature. Advancing knowledge 

 rendered a more satisfactory organization of the many kinds of 

 Hving things imperative. Thus the science of Taxonomy, or 

 classification, had its origin. In the past, classifications have been 

 based upon various features of animals and plants. To-day the 

 standard form is that based upon structure, because structural 

 resemblance seems to be the most constant and significant feature 

 in animal organization. Hence, Morphology and Embryology, and 

 with them Physiology, are important to Taxonomy. Zoogeog- 

 raphy, or the distribution of animals over the earth's surface, 

 and Paleontology, or the science of fossils, are not branches of 

 Taxonomy; but the classifier must consider the localities in which 

 existing animals are found and must have some knowledge of the 

 animals of the past. Beginning as a local effort to classify the 

 plants and animals of a neighborhood, classification was progres- 

 sively extended and developed into the science of Taxonomy. 



Variation and Heredity. — Variation may be defined, for pre- 

 Uminary purposes, as the differences between the individuals of a 

 species, and heredity as the resemblance between parents and 



