lO 



HUMAN ANATOMY. 



area or halo, the centrosphere or the attraction sphej-e, within which it appears as a 

 minute speck, frequently being double instead of single. 



In recapitulation, the chief constituents of the animal cell may be tabulated as 



follows : 



! Mesh work — Spongioplasm. 

 Ground-substance — Hyaloplasm, containing inclusions, Meta- 

 plasm. 



(Linin fibrils. 

 Chromatin (containing Nu- 

 clein). 

 Nuclear matrix (containing Paralinin^. 

 Nucleus \ Nucleolus (containing Pyrenin.) 



L Nuclear membrane. 



Protoplasm <{ 



V 



DIVISION OF CELLS. 



Disregarding for the present, at least, the occurrence of direct fission as a 

 means of producing new elements observed among the simplest forms of animal life, 



H 



Diagram of mitosis. /4, resting stage, chromatin irregularly distributed in nuclear reticulum; o, centrosphere 

 containing double centrosome; «, nucleolus. B, chromatin arranged as close spirem ; c, c, centrosomes surrounded 

 by achromatic radial striations. C, stage of loose spirem, achromatic figure forming amphiaster (amp). Z), chro- 

 matin broken into chromosomes ; nucleolus has disappeared, nuclear membrane fading ; amphiaster consists of two 

 asters (a, a) surrounding the separating centrosomes, connected by the spindle (s). E, longitudinal cleavage of the 

 chromosomes which are arranged around the polar field (p) occupied by the spindle. /^, migration of chromatic 

 segments towards new nuclei, as established by centrosomes (c,c); <»/i, equatorial plate formed by intermingling 

 segments. G, separating groups of daughter chromosomes (d. d) united by connecting threads (c t). H, daughter 

 chromosomes (rf, d) becoming arranged around daughter centrosomes which have already divided ; C C beginning 

 cleavage of cytoplasm across plane of equatorial spindle. /, completed daughter nuclei (£>, D) ; cytoplasm almost 

 divided into two new cells. {Modified from Wilson). 



or as an exceptional method among effete and diseased cells of the higher types, the 

 production of new generations of cells may be assumed as accomplished for all 



