COLLEGE ZOOLOGY 



standing water. They may swim about freely, 

 float on the surface, or crawl on the bottom, 

 and among the water plants. Each species 

 occurs in a definite type of minor habitat. 

 Such factors as the swiftness of the stream, 

 the character of the vegetation, the depth of 

 the water, and the nature of the bottom de- 

 termine what species of animals are present. 



Terrestrial animals 



We are more familiar with animals that 

 live on land than with aquatic species. Those 

 on land are called terrestrial animals. Many 

 live on the surface; others burrow beneath 

 the surface, thus becoming subterrestrial; 

 many make their homes in trees (arboreal 

 species) and in other plants; and a few, 

 known as aerial animals, spend a large part 

 of their time in the air. The surface-dwelling 

 animals may prefer either wet or dry ground, 

 humus, sand, or rocks. Subterrestrial animals 

 are profoundly influenced by the character 

 of the soil in which they live. Plant-dwelling 

 animals may live in evergreen (coniferous) 

 or in deciduous trees, on the bark or in the 

 wood, in dead wood or in living wood, on 

 the fruit or among the leaves. Aerial animals 

 may fly or simply glide through the air, or 

 may be carried about passively by some 

 balloonlike contrivance. 



Parasitic animals 



A parasite is an organism that lives the 

 whole or part of its life on or within another 

 organism of a different species, from which 

 it obtains its food. Parasites occur among 

 both plants and animals. Many animals that 

 live in water are parasitized by other animals 

 that creep over them or are attached to their 

 surfaces. Most parasites of terrestrial animals 

 live within the bodies of their victims; they 

 are inhabitants of the digestive tract, the 

 blood, and the muscle. Almost every large 

 group in the animal kingdom contains para- 

 sites, but the parasites are mostly protozoans, 

 flatworms, roundworms, annelids, insects, 

 mites, and ticks. 



Adaptations of animals 

 to their environment 



A study of the relation of animals to their 

 environment reveals many ways in which 

 they are adapted to the particular habitat 

 in which they flourish. These adaptations in- 

 volve all organs and all physiologic processes 

 that make up the activities of the animal. 

 Different animals are adapted to similar con- 

 ditions in different ways. Thus aquatic in- 

 sects and fish are able to move and breathe 

 under water, but the methods by which 

 these activities are accomplished are very 

 different. A review of the structure and be- 

 havior of any animal will show how wonder- 

 fully it is adapted to life in its particular ei> 

 vironment. Each species of animal, however, 

 is not adapted to a certain habitat to the ex- 

 clusion of other species— many species of 

 animals and plants may live in one habitat. 

 Animals, when associated together, form 

 what are known as animal communities. An 

 attempt has been made by students of ecol- 

 ogy to classify these communities. It is a 

 comparatively simple matter to determine 

 what species of animals occupy a certain 

 habitat, but it is more difficult to work out 

 the actual physiologic relations between the 

 animal and the various factors in its en- 

 vironment — only a beginning has been made 

 in this direction. 



Maintenance of the individual 



We have already noted that each species 

 of animal is limited to some particular type 

 of habitat. The problems involved in merely 

 existing in these habitats are many and 

 varied. In the first place, each animal must 

 protect itself from competitors, enemies, and 

 harmful physical agents. It must find proper 

 food and then capture and ingest it. Phys- 

 iologic processes within the body must 

 bring about digestion, transportation, and 

 assimilation of this nutritive material. Other 

 processes within the body must lead to lib- 

 eration of energy for the animal's various ac- 

 tivities. Oxygen must be taken in and carbon 



