A STUDY OF REPRESENTATIVES OF THE VARIOUS 

 ANIMAL PHYLA 



INTRODUCTION 



The preceding laboratory periods have been devoted to a study 

 of the organization of a moderately complex animal, the frog. 

 The grosser features of external structure were considered by 

 way of illustrating the importance of the surface of the animal, 

 especially as a means of providing a communicating and buffer 

 systems between the organism and its surroundings. The vari- 

 ous internal organs were studied with a view to ascertaining, first, 

 the services which they render and the manner in which it is 

 done and, second, the determination of the interrelationships 

 and interdependence of organs. It became apparent that the 

 body of the animal is an orderly association of components 

 organized according to a plan of differentiation resulting in 

 division of labor among the parts. This organization involves 

 all parts from the cells to the completed body. Each structural 

 component, whatever its rank, contributes a service in the organ- 

 ism as a whole but not independently. Each component in 

 contributing its service is assisted by other components. This 

 requires harmony of action or the coordination and control of 

 the various parts. Such coordination rests largely with the 

 nervous and hormonic forces. For example, respiration cannot 

 be considered as a function of any particular organ. There 

 are involved not only the services of the respiratory organs as 

 such but also the circulation, muscles, the surrounding medium, 

 nervous and hormonic activities, the internal environment, and 

 changes taking place in the protoplasm of the body. Respiration 

 is rather a function of the organism. And so it is with digestion, 

 excretion, etc. Thus it appears that the organism is a complex 

 of interactions taking place in relation with the protoplasm of the 

 component parts of the body and between it and the internal 

 and external environments. When life ceases the components 

 remain in the same state of organization as before death but what 

 is left is a corpse rather than an organism. That is, the inter- 



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