9° ZOOLOGY 



of stimtdus 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. If cells and organs become differentiated, and specialized 

 in the division of labor, it becomes doubly essential that they be 

 brought together again in a complete unity if there is to be an 

 efficient individual. This reintegration of diverse parts is (i) 

 physical, by means of connective and supportive tissues; (2) 

 chemical and nutritive, by means of secretions into the blood 

 and lymph ; and (3) cooperative, by means of the nervous system. 



10. 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 are homologous. They 

 are so called even though, because of their differing functions, 

 they are very different in appearance. 



116. Topics for Investigation, in Library and Field. 



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

 sion 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. 



3. Compare the ways in which animals known to you cap- 

 ture and prepare their food for swallowing. What special 

 structures arise in connection with this function ? 



4. Do animals have any power of storing food within the 

 body for future use ? Compare with plants. 



5. Compare gills and lungs as to general form and arrange- 

 ment and see in what ways they appear to you to be suited to 

 their particular media, i.e., gills to water and lungs to the air. 

 Why might not the conditions be reversed ? 



6. What seem to you to be the comparative advantages and 

 disadvantages of the exoskeleton and endoskeleton. 



7. Devices to accomplish locomotion in animals known to the 

 student. Find as many variations as possible. 



