104 ANIMAL LIFE 



tatoria and of others called Tardigrada, or bear-animalcules. 

 These bear-animalcules live in water. If the water dries 

 up, the animalcules dry up too ; they shrivel up into form- 

 less little masses and become desiccated. They are thus 

 simply dried-up bits of organic matter; they are organic 

 dust. Now, if after a long time years even one of these 

 organic dust particles, one of these dried-up bear-animal- 

 cules is put into water, a strange thing happens. The body 

 swells and stretches out, the skin becomes smooth instead 

 of all wrinkled and folded, and the legs appear in normal 

 shape. The body is again as it was years before, and after 

 a quarter of an hour to several hours (depending on the 

 length of time the animal has lain dormant and dried) slow 

 movements of the body parts begin, and soon the animal- 

 cule crawls about, begins again its life where it had been 

 interrupted. Various other small animals, such as vinegar 

 eels and certain Protozoa, show similar powers. Certainly 

 here is an interesting problem in life and death. 



When death comes to one of the animals with which 

 we are familiar, we are accustomed to think of its coming 

 to the whole body at some exact moment of time. As we 

 stand beside a pet which has been fatally injured, we wait 

 until suddenly we say, " It is dead." As a matter of fact, 

 it is difficult to say when death occurs. Long after the 

 heart ceases to beat, other organs of the body are alive 

 that is, are able to perform their special functions. The 

 muscles can contract for minutes or hours (for a short time 

 in warm-blooded, for a long time in cold-blooded animals) 

 after the animal ceases to breathe and its heart to beat. 

 Even longer live certain cells of the body, especially the 

 amoeboid white blood-corpuscles. These cells, very like 

 the Ammba in character, live for 'days after the animal is, 

 as we say, dead. The cells which line the tracheal tube 

 leading to the lungs bear cilia or fine hairs which they 

 wave back and forth. They continue this movement for 

 days after the heart has ceased beating. Among cold- 



