166 INTRODUCTION TO ZOOLOGY. 



nisli an explanation also for the cells that constitute 

 the different organs of our own bodies. The single 

 cell of the paramoecium is capable of performing all 

 the above named functions. When it contracts, it is 

 exercising the function of a muscle cell, and it is a 

 muscle cell. When it digests, it is a digestive cell. 

 When it respires, it is a respiratory cell. The muscle 

 ;Cell of the human body may be thought of as a cell, 

 like the protozoan cell, whose contractility has been 

 very much intensified and all other properties very 

 much diminished or held in abeyance or entirely lost. 

 So with a nervous cell. Its nervous character has 

 been very much -intensified and its contractility and 

 other properties entirely lost. The protozoan cell is, 

 as a cell, quite undifferentiated in its functions. 



Make a table showing resemblances between para- 

 mcecium, sponge, hydra, starfish, earthworm, clam, 

 grasshopper, and rabbit. 



Paramoecium ^ 



Sponge 



Hydra 



Starfish ( exchange CO3 for oxygen 



„ ., ) self-active movement 



Earthworm . , „ , . ,., ^. , 



^, 1 ingest food m sohd particles 



Clam ' 



Grasshopper 

 Rahbit 



From the above table, make a definition of an ani- 

 mal. What is your predicate noun? 



We are not able at this point to make a table of 

 differences between animals and jjlants. It is very 

 doubtful whether the above characteristics would 

 completely discriminate an animal from a vegetable. 

 But this is the best that we can do until we study 

 plants. Let us call these characteristics animal 

 characteristics. 



