n8 



MANUAL OF ELEMENTARY ZOOLOGY 



some other reason been removed from a human patient 

 has been used after several days to replace the same tissue 



in another man in which it 

 had been injured. 



Amoeba reproduces by the 

 process known as 



Reproduction. \. ,. 



binary fission, in 

 which first the nucleus and 

 then the cytoplasm parts asun- 

 der into two halves, each of 

 which appears, at all events, 

 to differ from the parent in 

 nothing but size. In some 

 species of Amoeba the division 

 of the nucleus is amitotic, but 

 in Amoeba proteus there is a 

 peculiar kind of mitosis in 

 which the place of centro- 

 somes is taken by a mass of 

 clear protoplasm at each end 

 of thernicleus. These masses 

 are known as, pole plates and 

 arise within the nuclear mem- 

 brane, which does not break 

 up during division as in ordin- 

 ary mitosis. 1 After the divi- 

 sion of the nucleus the cyto- 

 plasm flows apart into two 

 bodies, each of which contains 

 one of the daughter nuclei. 

 The new bodies are at first 



Fig. 73.— Multiple fission of 

 Amoeba proteus. — After Scheel. 



Amceba encysted ; b, section of a connected by a bridge of 



cyst in which numerous nuclei have protoplasm, but this becomes 

 been formed ; C, surface view of a . T . , . 



ripe cyst in which the spores are narrower until it breaks 



beginning to separate and the cyst through and tWO new indi- 

 wall to break up ; Z>, a single spore . , ° . . 



highly magnified. viduals come into being. An- 



other kind of fission, known 

 as multiple fission or spore formation, has been seen in 



1 Not all the chromatin in Amceba proteus forms chromosomes. That 

 of the outer part of the nucleus behaves as in amitotic divisions. There 

 is an inner mass which alone takes part in the mitotic process. 



