PROTOPLASM AND THE CELL 



59 



tain of the single-celled blood parasites are about as small as any 

 cells known. They are barely seen with our highest magnifications. 

 At the other extreme of size we may refer to another parasitic 

 single-celled animal, Porospora gigantea, which lives in the intestine 

 of the lobster, and may reach from one-half to two-thirds of an 

 inch in length. Egg cells, including the yolk, may exceed this size. 

 Some of the nerve cells, though of less mass, may be several feet 

 in length. Muscle cells are relatively long also. 



Plasma /Atmirane 

 Eciop/asm 

 Chondriosoma 

 En</op/asm 



Lin in 



Chromaf/n 

 Mucf^us 



Nucteof Sap 

 Vcict/o/e 



A/</c/zar Membrane 



Plastid 



Fig. 20. — Diagram showing a typical animal cell. 



The shape of the typical cell is spherical; but due to the effects 

 of mechanical pressure, specialized functions, and unequal growth 

 almost all cells are far from this shape. They vary greatly in shape 

 and include platelike, cubical, columnar, polygonal, and spindle- 

 shaped forms. The particular form of any cell is not a haphazard 

 matter but strictly controlled by morphological and functional 

 necessities. 



