THE GENERAL ANIMAL FUNCTIONS. 8l 



tive processes. Growth is increase in mass ; reproduction is 

 the production of new individuals from old. Reproduction 

 always involves cell division and may be asexual or sexual. 

 The latter normally involves two parents. In it two cells, 

 which may be either similar or dissimilar, must unite before 

 development will proceed. 



7. The nervous and muscular systems are closely related 

 in function. Their united work is to receive, coordinate and 

 respond to the external or internal stimuli affecting the ani- 

 mal. The structures to receive stimuli (end organs) are 

 largely superficial; the coordinating and controlling parts 

 (central organ) are deep-seated, thereby securing protection 

 and a central position ; the muscular system must have definite 

 relations with the hard parts upon which it acts. Thus arises 

 the necessity of connectives or nerves between the various 

 portions. 



8. The sense organs represent areas of the epithelium which 

 are peculiarly adapted to the reception of some one of the 

 forms of stimulus to which animals are subject, supplemented 

 by a more or less complex apparatus which serves to intensify 

 or modify the original stimulus. The sense organ determines 

 the kind of stimulus which may be received, but the central 

 nervous organ determines the nature of the sensation which 

 results, and the response. 



9. Organs with different origin which by reason of similar 

 function have come to look alike are said to be analogous. 

 Organs with similar origin and structure, even though they 

 may appear differently because of their differing functions, 

 are homologous. 



112. Topics for Investigation, in Library and Field. 



1. What are the advantages and the disadvantages of divis- 

 ion of labor and differentiation? Illustrate your views very 

 fully. 



2. Illustrate the variety of foods used by different animals 

 with which you are acquainted. Classify the animals you 

 know on the basis of their food preferences. 



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