104 



MANUAL OF ELEMENTARY ZOOLOGY 



by 



of 



a delicate nuclear membrane and appears to consist 

 a viscid meshwork with a thinner fluid in its 



interstices (see 

 p. 85). The viscid 

 nuclear sub- 

 stance, or linin, 

 forms, on the 

 emulsion theory 

 (p. 85), the walls 

 of minute bubbles 

 in which the thinner 

 fluid, or nuclear sap, 

 is held. In the 

 linin lie granules of 

 the deeply-staining 

 substance chroma- 

 tin. There is often 

 also a body known 

 as the nucleolus, 

 consisting of a sub- 

 stance which stains 

 differently from 

 chromatin. Out- 

 side the nucleus 

 lies a minute body 



leu. 



Fig. 63. — Blood of a frog, highly magnified. 



A, Fresh; B, stained. 



leu., Leucocytes ; r.c, red corpuscles. 



known as the cen- 

 trosome. When mi- 

 tosis is about to 

 take place, the cen- 

 trosome divides 

 into two halves 

 which travel to 

 opposite sides of the 

 nucleus. As they 

 separate, the proto- 

 plasm becomes ar- 

 ranged in a radiating 

 manner around each, 

 forming a figure 

 known as the aster. Fig 

 Meanwhile the nu- 



leu. 



64. — Human blood, highly magnified. 

 leu., Leucocytes; r.c, red corpuscles. 



