CHAPTER 6 

 CELLS OF THE VERTEBRATE BODY 



In the preceding chapters the functions of metabolism, irrita- 

 bihty, and reproduction in the vertebrate organism were dis- 

 cussed. Such a consideration of function, together with that of 

 the structure or anatomy of the vertebrate, conveys a rather 

 definite idea concerning the animal as an individual, possessing the 

 complex and highly coordinated organization that is familiar in 

 the higher types. It is evident, however, that in order to explain 

 the outward manifestations of Hfe one must understand the activ- 

 ities that are characteristic of protoplasm as it occurs in the animal 

 cell. The individual organism is an association of cells, which make 

 up its structure and determine its functions by their correlated 

 interdependence. A fundamental understanding of cells is neces- 

 sary for the explanation of the normal morphology and physiology 

 of the individual. It is also true that the appearance of cells 

 furnishes the evidence that enables us to analyze and classify the 

 abnormal conditions which exist in diseased organisms, and which 

 are determined by the science of Pathology. 



As will be pointed out in the chapters on development, the 

 processes whereby the adult individual arises from the germ cells, 

 through all the stages of cell division and differentiation, are, essen- 

 tially and without exception, cell phenomena. Embryology is 

 best understood as the behavior of cells during the development of 

 organisms. In addition, the subject of Genetics, or the study of 

 heredity and variation, can be explained satisfactorily only when 

 one makes clear the cell phenomena that are correlated with the 

 inheritance of characteristics from generation to generation. 

 Hence, the science of Cytology, which deals with all aspects of cell 

 structure and activity, explains phenomena in all fields of biological 

 investigation. For the student of General Zoology, this funda- 

 mental knowledge of cells is best obtained through the detailed 

 consideration of a particular subject. In the present chapter the 



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