CHAPTER XXXIX 

 THE ANIMAL SERIES 



263. We have already learned from our study of plants 

 that they vary in size and structure from the one-celled 

 bacteria to the many-celled giant trees of the forest. Ani- 

 mals also vary in number of cells and complexity of 

 structure from the one-celled microscopic animals to the 

 largest and most complex type. This chapter gives a 

 general view of the animal life of the world by studying 

 the animals in groups arranged approximately according 

 to their complexity. All animals can be divided into two 

 groups the one-celled animals and the many-celled 

 animals. The many-celled animals can be divided into 

 a great many subdivisions, such as worms, insects, crus- 

 tacea, fish, amphibia, reptiles, birds, and mammals. 



264. Protozoa or One-celled Animals. -- There are 

 many one-celled animals which can be found in stagnant 

 water such as that found in swamps or ponds. There 

 are two one-celled animals which can be easily found and 

 of which we shall here make a careful study. The simpler 

 of these two is the amoeba. It is a mass of protoplasm, 

 somewhat granular in structure, which has no definite form 

 or shape and moves about by putting out projections, and 

 when it encounters any food, such as bacteria, it rolls 

 itself about them and thus takes the bacteria within its 

 own protoplasmic body. It absorbs the food value of 

 the bacteria and discards the waste matter chiefly through 

 the part of its body called the contractile vacuole. 



