THE VERTEBRATE ANIMAL — SUBPHYLUM VERTEBRATA 377 



The vertebrate animal is covered by an integument or skin which 

 serves as a protective and sensorj- organ. It also helps in excretion 

 through the sweat glands, mucus glands, and oil glands as well as 

 facilitating temperature regulation in some. Such exoskeletal struc- 

 tures as scales, nails, hoofs, claws, feathers, hairs and enamel of 

 teeth are produced by the skin. The integument is composed of an 

 outer stratified epithelial epidermis which consists of several layers 

 of cells, few nerves, and no blood vessels, and the inner fibrous dermis 

 or corium, which consists of areolar connective tissue, nerves, nerve 

 endings, integumental glands, blood vessels and lymph spaces. The 

 membrane type of bone is developed in the dermis. 



The maintenance of any living body requires the cooperation of 

 several functions which will attain similar fundamental results 

 wherever in living material they occur. The principal functions 

 performed by the structures in the animal body are: (1) support 

 and protection, (2) movement and locomotion, (3) digestion, (4) 

 respiration, (5) circulation, (6) excretion, (7) reproduction, (8) 

 reception and conduction of stimuli, and (9) internal regulation. 

 These functions merge into one living process which involves the 

 building up of protoplasm, transformation of energy, and repro- 

 duction. During the execution of these activities energy is con- 

 stantly being changed from the potential to the kinetic form. 



Metabolism. — The collective term metabolism is employed when re- 

 ferring to all of the interactions involved in the living process of pro- 

 toplasm. It includes the processes concerned with conversion of food 

 into protoplasm, release of energy through oxidation, production of 

 heat, movement, elimination of wastes ; or, in other words, these proc- 

 esses are chiefly : Ingestion, digestion, egestion, absorption, transporta- 

 tion, respiration, oxidation, and elimination. The processes concerned 

 with the conversion of food material into protoplasm (building up) 

 constitute the phase of metabolism known as anaholism. Included 

 here are ingestion, digestion, absorption, transportation, and assimila- 

 tion. The oxidation of materials of the protoplasm to liberate energy, 

 and the elimination of wastes incidental to it, is known as cataholism 

 or the "breaking down" phase. 



Metabolism is one of the fundamental features of all protoplasm, 

 therefore, all physiology, since it is a study of the functions of liv- 

 ing organisms, must be concerned with metabolism. It includes all 



