138 



PROTOZOOT-OGY 



posterior individual is reversed so that the posterior end of the 

 parent organism becomes the anterior end of the posterior 

 daughter individual. In the ciliate Bursaria, Lund (1917), ob- 

 served reversal of polarity in one of the daughter organisms at 

 the time of division of normal individuals and also in those which 

 regenerated after being cut into one-half the normal size. 

 In the Ciliophora the division is as a rule transverse (Fig. 48), 



^ 



''4 





Fig. 63. External morphological changes during division of Amoeba 

 protetis, as viewed in life in reflected light, X about 20 (Chalkley and 

 Daniel), a, shortly before the formation of the division sphere; b, a 

 later stage; c, prior to elongation; d, further elongation; e, division al- 

 most completed. 



in which the cytostome without any enlargement or elongation 

 divides by constriction through the middle so that the two 

 daughter individuals are about half as large at the end of division. 

 Both individuals retain their polarity except in a few cases. 



Multiple division. In multiple division the body divides into a 

 number of daughter individuals, with or without residua^ cyto- 

 plasmic masses of the parent body. In this process the nucleus 

 may undergo either simultaneous multiple division, as in Ag- 

 gregata, or more commonly, repeated binary fission, as in Plasmo- 

 dium (Fig. 198) to produce large numbers of nuclei, each of which 



