344 



ANIMAL LIFE 



itself and divides into several fragments. The cyst then 

 burst, and each fragment or spore becomes a separate 

 animal. As noted in a previous chapter, budding takes 

 place in the hydra and many other coelenterates and in a 

 fow worms. Reproduction by eggs occurs in all species 



above the protozo- 

 ans. The eggs and 

 spores of some of 

 the microscopic ani- 

 mals are so small 

 as to require very 

 high magnifying 

 power to define them 

 clearly, and when 

 dry are capable of 



inthe air by currents 



thereby gaining access to open vessels of water or other 

 fluids suited to their development. Until fifty years ago 

 people thought that broth or milk boiled in an air-tight 

 jar sometimes spoiled because particles of the materials 

 were transformed into minute living bodies. At present 

 it is well understood that the life in the sealed and heated 

 jars was due to minute germs or spores of plant life, called 

 bacteria, some of which are not killed by being boiled a 

 half hour. 



Up to the present time nearly a half million different 

 kinds or species of animals have been described, and more 

 than a hundred new species are discovered every year, so 

 that it is probable that there are no less than a million 

 species of animals dwelling on this planet. That a pair of 



