196 Education through Nature 



is due to specific chemical substances in the two 

 cases. 



Structure of the Cell. 



In the amoeba there is scarcely any visible evidence 

 of structure, even under the highest power of the 

 microscope; the form is constantly changing; there 

 seems to be no bilateral symmetry or fore or aft polar- 

 ity; and even the protoplasm itself is constantly 

 flowing like a turbid stream of liquid substance. In 

 the paramecium, on the contrary, there is both per- 

 manent form, fore and aft polarity, and bilateral 

 symmetry. Here, too, the protoplasm shows a stream- 

 ing motion. By staining these organisms with various 

 dyes, an internal spherical body called the nucleus 

 is revealed, showing that, notwithstanding the appar- 

 ent homogeneity, there are specialized areas within 

 this protoplasm, suggesting organs, and hence a 

 heterogeneity of composition, at the basis of which 

 some primitive structure must exist. In many cells 

 another modified area, having still more the character- 

 istics of structure, has been found; and, for that rea- 

 son, it is now one of the most interesting little bodies 

 in nature. It is called the centrosome. Under the 

 highest power of the microscope it looks like the dot 

 of the letter i, yet in this little dot is centered one of 

 the profoundest issues with which biologists have to 

 deal. The issue is none less than that of form 'versus 

 substance, heredity versus variation. A valuable 

 book on this subject is one by E. B. Wilson entitled 

 " The Cell in Heredity and Development." Those 

 who are interested in these profound biological prob- 

 lems will find that work very helpful. The subject 

 cannot be treated in a work of this kind. 



Life Phenomena of Cells. 



Nothing is more evident, from the examination of 

 the micro-organisms in our jar of stagnant water, 



