THE ANIMAL CELL. 



[CH. II. 



CHAPTER II. 



THE ANIMAL CELL. 



AN animal cell is usually of microscopic dimensions, in the 

 human body varying from -^Q to 30 1 00 of an inch in diameter. 

 It consists of 



1 . Protoplasm. This makes up the main substance of the cell. 



2. Nitcleus : a vesicular body within the protoplasm, generally 

 situated near the centre of the cell. 



3. Centrosome and attraction sphere : these are contained within 

 the protoplasm, near the nucleus. 



These three portions demand separate study. 



Protoplasm. 



Until recent years, protoplasm was supposed to be a homo- 

 geneous material entirely destitute of structure, though generally 

 containing minute granules of solid consistency, or globules 

 (vacuoles) containing a watery fluid. 



It has, however, now been shown with high powers of the 

 microscope that in many cells the protoplasm consists of two 



Fig. 6. (A.) A colourless blood-corpuscle showing the intra-cellular network, and two 



nuclei with intra-nuclear network. 



(B.) Coloured blood-corpuscle of newt showing the intra-cellular network of 

 fibrils. Also oval nucleus composed of limiting membrane and fine intra- 

 nuclear network of fibrils, x 800. (Klein and Noble Smith.) 



parts, a fine network of fibrillfe in which the more fluid and 

 apparently structureless portion of the protoplasm is contained. 

 (See figs. 2 and 6.) 



The network or spongework is called the reticulum or 

 spongioplasm, and the more fluid portion in its meshes the 

 enchylema or hyaloplasm. 



