512 



COLLEGE ZOOLOGY 



fested by all animals, but it is particularly 

 obvious in the "warm-blooded" birds and 

 mammals. Chemical energy takes part in the 

 building up and breaking down of proto- 

 plasm within cells (metabolism). Light 

 energy is exhibited by a few animals but in 

 small quantities. For example, it takes 2000 

 fireflies flashing simultaneously to produce 

 the illumination of a single candle. Electric 

 energy in very small amounts is involved in 

 all of the activities of living cells, but may 

 become concentrated as in certain fish such 

 as the torpedo ray or the electric eel. 



During photosynthesis radiant energy is 

 absorbed and transformed into the potential 

 chemical energy of organic compounds. Al- 

 though practically all our energy is obtained 

 from these organic compounds, a very small 

 amount appears to be received directly from 

 the sun and is utilized in the manufacture of 

 vitamin D in the skin from sterols; this is of 

 importance from the standpoint of general 

 health. Most of the radiant energy which we 

 receive daily from the sun eventually be- 

 comes transformed into heat which is 

 quickly dissipated. 



Types of nutrition 



Animals and plants that carry on photo- 

 synthesis are said to be holophytic. Most 

 animals feed on solid material, and nutrition 

 involving the ingestion of such matter is 

 called holozoic. Many animals, especially 

 parasites that live within the bodies of other 

 animals, absorb organic substances in solu- 

 tion through the surface of their body; this 

 type of nutrition is termed saprozoic. 



Classification of animals 

 according to their diet 



Three principal types of animals may be 

 recognized, based on their diets: herbivor- 

 ous, carnivorous, and omnivorous. Herbi- 

 vorous animals feed on vegetation and are 

 adapted for that purpose. For example, leaf- 

 eating insects possess chewing mouth parts; 

 seed-eating birds may have short, thick bills 



for breaking hard seeds; rabbits and other 

 rodents are provided with sharp incisor teeth 

 suitable for gnawing; and ruminants such as 

 cattle have enormous stomachs of several 

 chambers for storage of vegetation. 



Carnivorous animals live on animal food. 

 One order of meat-eating mammals is 

 named Carnivora, but many mammals be- 

 longing to other orders also eat meat. Such 

 mammals often have enlarged canine teeth 

 for holding their prey. Many of the types we 

 have studied are carnivorous: paramecia eat 

 other protozoans, coral polyps ingest only 

 animal food; spiders and leeches suck up 

 animal juices; and lampreys, dogfishes, 

 perches, frogs, and some turtles all live on 

 animals. 



Omnivorous animals feed on both animal 

 and vegetable matter. Many protozoans eat 

 both miscroscopic plants and animals, as do 

 also fresh-water mussels; earthworms feed 

 largely on decaying vegetation but also in- 

 gest animal food; and the greatest of all 

 omnivores is man himself. 



Food capture 



Most animals that are capable of locomo- 

 tion move about "seeking whom they may 

 devour"; but a few species are sedentary and 

 must either wait for food to come to them, 

 or they possess some method of bringing it 

 into range. The oyster, for example, becomes 

 attached to some solid object by the left 

 valve of its shell when very young, and the 

 organic particles that constitute its food are 

 drawn into the shell in currents of water 

 created by the beating of cilia on the oyster's 

 body. Sponges obtain their food in a similar 

 manner. 



Among the protozoans, food may be cap- 

 tured by means of pseudopodia, flagella, or 

 cilia. Tentacles provided with nematocysts 

 are characteristic of the coelenterates. Star- 

 fishes include bivalve mollusks among their 

 prey, and are able to open their shells by a 

 long, steady pull with their tubefeet. Many 

 spiders build webs for capturing insects. 

 The frog accomplishes the same thing with 



