CHAPTEE II 



THE ANIMAL CELL 



AN animal cell is usually of microscopic dimensions, in the human 

 body varying from y^ to -g-^Vo- of an inch in diameter. 

 It consists of 



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



2. Nucleus: 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 homogeneous 

 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 micro- 

 scope that in many cells the protoplasm consists of two parts, a fine 



FIG. 6. (A.) A colourless bioud-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 uf limiting membrane and fine intra-imclear network of fibrils, x 800. 

 (Klein and Noble Smith.) 



network of fibrillse in which the more fluid and apparently structure- 

 less portion of the protoplasm is contained. (See figs. 2 and 6.) 



