10 



A COURSE ON ZOOLOGY. 



FIG. 1. 



A cell is a little mass having a varying form, generally 

 spherical or ovoid, and made up of a jelly-like matter 



that is called 

 protoplasm. In 

 this protoplasm 

 is distinguish- 

 able a parti- 

 cle somewhat 

 denser than the 

 rest, and this is 

 the nucleus of 

 the cell. It is 

 like the stone 

 A, cell and typical nucleus: a, slight membrane; of a cherry SUr- 

 b, radiating protoplasmic net- work ; c, wall of nu- , , , , 



cleus; d, plasma of nucleus; e, nuclear coil. B, DV l 



nucleus at rest, showing net-work. C, nucleus softer fruity 

 before division, showing coiled filament. matter These 



cells are always so small that they cannot be seen with- 

 out the aid of a powerful microscope. 



We have said that the cell is the fundamental element 

 of all tissues, that is, the cell in some one or other of 

 its modifications produces the elements which are grouped 

 together in the various tissues. 



Sometimes the cell is elongated like a slender reed, 

 this is a fusiform cell; sometimes it is star-shaped, and 

 is said to be stellate. Or it may be thread-like, form- 

 ing a fibre, or drawn out into a hollow filament, called 

 a tube. All these elements possess peculiar properties, 

 and according to their forms and their properties they 

 have received different names. These names are also 

 given to the tissues which they constitute. Muscular 

 tissue is composed of little bundles of fibres, which ap- 

 pear striated under the microscope. Nervous tissue is 



