CHAPTER IV 



THE RHIZOPODA— AMffiBA PEOTEUS 



Our studies have hitherto been directed to the elucidation of 

 the anatomy and development of a complex animal provided 

 with tissues and organs which subserve different purposes in 

 its economy, and are modified structurally in accordance with 

 the functions which they have to perform. We have seen that 

 all its tissues (which are comparable to our own) are formed 

 either by, or out of, certain ultimate form-elements called cells, 

 and that the diversity and complexity of the animal's structure 

 is to be referred to the diversity of structure obtaining among 

 its component cells. Further, we have seen that this remark- 

 ably complex animal, composed of countless cells, is brought 

 into being from the simplest possible beginning — namely, a 

 germ-cell, which, after undergoing the processes which have 

 been described as maturation and fertilisation, possesses the 

 power of giving rise to the entire organism. The course of 

 the development of the germ-cell has only been lightly touched 

 upon ; but we have seen that it consists essentially in the 

 multiplication of the fertilised germ-cell or oosperm by division, 

 the products of division cohering and forming a hollow embryo 

 composed of many cells, which are ultimately differentiated to 

 form the tissues of the adult. 



We have learned in the course of these studies that all the 

 phenomena of the frog's life (exclusive of its psychical pheno- 

 mena, which baffle our powers of analysis) are to be referred 

 to the activities of its cells. We now can turn to the study 

 of a large group of organisms of the simplest possible con- 

 stitution, the Protozoa, whose vital phenomena are manifested 

 within the limits of a single cell. 



In commencing the study of the Protozoa, we cannot do 

 better than begin, as is customary, with the study of a common 

 pond animalcule, known to science by the name of Amoeba 

 proteus. This minute organism, pregnant with meaning to 



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