AN INTRODUCTION TO ZOOLOGY 



(i) During binary division the nucleus apparently divides ami- 

 totically, although indications of mitosis have been reported. A 

 definite mitotic figure is formed in certain species of Ameba, 

 e.g. Ameba binudeata (Fig. 17). While the nucleus is elongating, 

 a constriction appears around the middle of the cell; the nucleus 

 then separates into two apparently equal parts which move 

 toward the ends of the animal. Meanwhile the constriction of 



the body has grown deeper, and finally 



severs the connection between the two 

 ends, and two daughter Amebae result 

 (47, Fig. 16). 



(2) Scheel (46) seems to be the only 

 person who has ever witnessed sporulation 

 in Ameba proteus. The whole process 

 lasted from two and one half to three 

 months. The pseudopodia were first 

 drawn in and the animal became spher- 

 ical. A three-layered cyst was then 

 secreted. The Ameba rotated within this 

 for several days, after which all move- 

 ments ceased. The nucleus divided until 

 there were twenty or thirty present, 

 arranged near the surface. Continued 

 division resulted in an increase of nuclei 

 to from five hundred to six hundred. 

 The central part of the body had 

 none. Cell walls now appeared at the periphery, cutting 

 off the nuclei, each with a small amount of the surrounding 

 cytoplasm. The wall of the cyst became soft, broke, and 

 allowed the small Amebae to escape. Hundreds of these 

 Amebulae, or pseudopodios pores, as they are sometimes called, 

 broke out at one time. They became recognizable as Ameba 

 proteus in from two and a half to three weeks. No reason 

 could be discovered for sporulation, although experiments were 

 conducted in which specimens were starved, were given an excess 



FIG. 17. Ameba binu- 

 deata beginning to di- 

 vide. Both nuclei have 

 formed mitotic figures. 

 (From Lang after 

 Schaudinn.) 



