38 ELEMENTARY ZOOLOGY. 



50. Gross Organization. It is not the purpose here to 

 discuss all the organs and parts that appear, with a little 

 study, to belong to animals and plants. It is sufficient 

 to notice that there is a tendency among living things 

 to become bounded by curved surfaces, to have different 

 structures developed at different parts of the body, 

 which enable us to distinguish one end, or surface, or 

 side, from the others. This differentiation is essential to 

 organization and is one of the most marked features of 

 any object that has been produced by the agency of life. 



FIG. 2. 



FIG. 3. 



FIG. 2. Diagram showing "organization" within the cell, and something of the 

 structure of the protoplasm, as it might appear while living, a, alveoli or spheres in 

 the semifluid substance; c, centrosome; cy, cytoplasmic (protoplasmic) meshwork, 

 containing granules; nu, nucleus; n, nucleolus; v, vacuole; w, cell wall. 



FIG. 3. Diagram showing the principal parts of the cell as it appears after it is 

 killed with chemicals. The protoplasm shows more of a meshwork (cy). The spaces 

 represent the alveoli. /, formed substance in the alveoli. Other letters as in Fig. 3. 



Questions on Figures 2 and 3. If these cells are in reality 2 5^ in di- 

 ameter, how much are they enlarged in the drawing?(M is .001 mm.). 

 Identify the various structures mentioned in section 51. 



51. Cellular Organization. In all our larger organisms 

 the differentiation does not stop with this surface condi- 

 tion. Living objects, above the very lowest, are made 



