GENERAL ORGANOLOGY. 157 



shape and to the performance of a single function ; conse- 

 quently every organ is characterized morphologically (ac- 

 cording to its structure and its relations and physiologi- 

 cally (according to its function). 



2. Organs of different animals may be physiologically 

 equivalent, analogous organs (i.e., with similar functions). 



3. Organs of different animals may be morphologically 

 equivalent, homologous (developing in similar relations). 



4. In the comparison of the organs of two animals 

 three possibilities become evident. 



a. They may be at the same time homologous and 

 analogous. 



b. They may be homologous, but not analogous (swim- 

 bladder of fishes, lungs of mammals). 



c. They may be analogous, but not homologous (gills 

 of fishes, lungs of mammals). 



5. Organs are divided into animal and vegetal.. 



6. Animal functions are those which are not completely 

 foreign to plants, but in them are only slightly developed; 

 in the animal kingdom, on the contrary, they undergo an 

 increase and become characteristic. 



/. Vegetal functions are developed with equal com- 

 pleteness, though in a different manner, in plants and 

 animals. 



8. To the animal organs belong the organs of movement 

 and sensation, such as the muscles, the sense-organs, the 

 nervous system. 



9. To the vegetal organs belong the organs of nutri- 

 tion and reproduction. 



10. Under nutrition, in the widest sense, are included 

 not only the taking in and digestion of food and drink, but 

 also the taking in of oxygen (respiration), the distribution 

 of food to the parts of the body, and the removal of matter 

 which has become useless. 



11. With nutrition, therefore, are concerned not only 

 the digestive tract and its accessory glands, but also the 

 organs of respiration, the blood-vascular system, and the 

 excretory organs (kidneys). 



