SECTION III. 



The Tissues. 



All the tissues of the body are formed from a single cell — 

 the ovum. 



In unicellular organisms the functions of nutrition and 

 of reproduction are performed by the one cell. In the 

 metazoa there is a ditierentiation into gametic or reproductive 

 cells, and somatic or body cells which form the various- 

 tissues of the individual. The latter are primarily developed to 

 nourish and protect the gametic cells which are potentially 

 eternal, going on from generation to generation, while the 

 somatic cells perish with the death of the individual. 



The mammalian ovum is holoblasdc and undergoes com- 

 plete division. The cells get arranged in three layers, the 

 epiblast, mesoblast, and hypoblast, and from these the 

 tissues are developed. 



The structure of the tissues must be studied practically 

 in the class of Histoloofv. Here all that will be given is a 

 brief summary of their development, and of their structural 

 and chemical characters. 



(A) THE VEGETATIVE TISSUES. 



The Vegetative Tissues are those which support, bind 

 together, protect, and nourish the body. They may be 

 divided into the Epithelial Tissues, formed from the epiblast 

 or hypoblast, and consisting of cells placed upon surfaces, 

 and the Connective Tissues developed from the mesoblast, 

 and consisting chiefly of formed-material between cells. 



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