192 



GENERAL PHYSIOLOGY 



unicellular organisms and leucocytes, has been met with only 

 in very few forms of cells. The division of Ammba can serve as a 

 type (Fig. 71). While the Amoiba is creeping, the original 

 spherical nucleus becomes gradually lengthened, then biscuit- 

 shaped, then constricted through the middle ; the connecting- 

 piece becomes constantly slenderer and finally breaks ; and thus 

 two new nuclei result, which immediately assume the spherical 

 form. Then the division of the protoplasm begins ; the Ammba 







Fig. 71. — Amt^eba polypodia in six successive stages of division The dark body surrounded by a 

 clear area in the interior is the nucleus, the pale body the contractile vacuole. (After F. E. 

 Schulze.) 



becomes constricted in a similar manner between the two nuclei 

 like a dumb-bell and creeps towards the two sides, until only a 

 thin thread of protoplasm unites the two halves , this finally breaks 

 so that two new Ammbce, each with one nucleus, result from the 

 division. The process requires a long time, usually several hours, 

 and does not always proceed smoothly : the protoplasm often flows 

 together into one mass after a considerable constriction has 

 taken place, and then flows apart again, until, finally, the uniting 

 bridge is torn through. 



