VITAL ANIMAL LIFE PROCESSES 69 



in water, the problem can be solved by simple diffusion of dissolved 

 products from one part of the body to another, but as the animals be- 

 come larger such a method cannot suffice. Blood and lymph are the 

 agents which serve to carry substances from one part of the body to 

 another in the higher animals. These body fluids, however, are of no 

 value as media of transportation unless they are moving. In the higher 

 animals pumping mechanisms called hearts keep the fluids in constant 

 motion. In animals intermediate between the one-celled animals and 

 these higher forms, there is a variety of mechanisms of transportation. 

 In jellyfish and flatworms the digestive system branches to all parts of 

 the body and serves as a means of distribution. The starfish which lives 

 in the ocean actually takes sea water into its body and circulates it to 

 all five arms. Insects have blood vessels which carry the blood from 

 the heart to all parts of the body, but no vessels to bring it back — it 

 collects in cavities and finally accumulates in a space around the heart. 

 But whatever the method used, transportation of materials throughout 

 the body is a necessary life process. 



Reproduction 



Although this life process is not absolutely essential for the existence 

 of an individual, it is certainly necessary for the continued existence of 

 the species. Even in a complex animal like a human being, it is pos- 

 sible to remove the reproductive organs and have life continue. All 

 animals, however, are faced with the certainty of the termination of 

 their lives as individuals. Every species, therefore, must have some 

 way of producing new animals like themselves, if the race is to con- 

 tinue to exist. 



The simplest method of reproduction is known as fission. By this 

 process an animal divides itself into two parts and each part continues 

 to grow as a separate individual. This method is found in the one- 

 celled animals and some of the simple worms. An animal with this 

 method of reproduction does not grow old and die — it grows and divides. 

 Nevertheless, its life as an individual is terminated when it splits in 

 two and begins existence as two separate organisms. 



Closely related to this is the method of reproduction known as 

 budding. Small buds appear as outgrowths from the body of an animal, 

 and these grow until they form a mature individual. Sometimes the 

 buds break off to form separate animals and sometimes they remain 

 attached so that a cluster of animals remains together to form a colony. 

 Some of the jellyfish are formed by the first method and some of the 

 sponges by the second. Since there is no union of animals or cells in 



