96 ELEMENTARY ZOOLOGY. 



9. The special sense organs, as the retina of the eye, 

 the taste cells, the sensitive cells of the inner ear, and the 

 like, are made up of protoplasm which has developed 

 one form of sensitiveness at the expense of other kinds. 

 Naturally the senses have arisen in adjustment to those 

 external stimuli which are most powerful in their influence 

 on life. We do not have sense organs giving knowledge 

 of general external conditions that have no power to 

 mold life. The more complex of these senses have, 

 beside the sensory part, certain structures which intensify 

 or otherwise modify the original stimulus. This is seen 

 in the lens and iris, etc., of the eye. 



1 01. Supplementary Topics for Themes in Zoology or 

 English. i. Why is the plan of dividing up the work to 

 be done, among special organs, better than having the 

 whole organism doing all the work, as in the one-celled 

 animals? Are there any disadvantages in this division 

 of labor? 



2. Compare the ways in which animals known to you 

 capture their food and prepare it for swallowing. Enu- 

 merate the special structures that different animals 

 have to enable them to do this. 



3. To what extent and in what ways may foods be 

 stored in the animal body for future use? Compare with 

 plants in this respect. 



4. Why can gills not be used satisfactorily in the air, 

 nor lungs by water-breathers? 



5. The special advantages of having the hard parts of 

 an animal on the outside rather than the inside. The 

 disadvantages. 



6. The problems which a moving animal has may be 

 stated as follows: (i) support in the medium, against 

 the pull of gravity; (2) the displacing the medium in 



