GROWTH, REGENERATION AND REPRODUCTION 



1113 



It has been shown that the number of chromatic loops differs 

 greatly in different animals but is constant in the same species. Man 

 has sixteen chromosomes in the nucleus of his somatic cells, while the 

 mouse and salamander have twenty-four, those of Ascaris two or 

 four, and those of the crustacean Artemia one hundred and sixty- 

 eight. It appears, therefore, that mitosis effects a meristic division of 



Fig. 531. — Metaphase and Anaphases of Mitosis in Cells (Spermatocytes) of the 



Salamander. 



E, Metaphase. The continuous central spindle-fibers pass from pole to pole of the 

 spindle. Outside them the thin layer of contractile mantle-fibers attached to the di- 

 vided chromosomes of which only two are shown. Centrosomes and asters. F, Trans- 

 verse section through the mitotic figure showing the ring of chromosomes surrounding 

 the central spindle, the cut fibers of the latter appearing as dots. G, Anaphase; diver- 

 gence of the daughter-chromosomes, exposing the central spindle as the interzonal 

 fibers; contractile fibers (principal cones of Van Beneden) clearly shown. H, Later 

 anaphase (dyaster of Flemming) ; the central spindle fully exposed to view; mantle-fibers 

 attached to the chromosomes. Immediately afterward the cell divides. {Drilner.) 



the chromatin of the mother-cell, so that the daughter-cells may be 

 equally provided with this material. Amitosis, on the other hand, 

 presents itself rather as a division of mass. 



Regeneration. — Besides growth, an organism has two duties to 

 perform, namely, to reproduce the cells which have been used up in 

 its processes of life, and secondly, to reproduce its like in the form of 



