64 



MULTIPLICATION OF PROTOZOA 



with its axoneme, are formed. The body of the flagellate then divides 

 longitudinally from before backwards in a dorso-ventral plane between 

 the two dorsal membranes. Owing to the blepharoplasts being situated 

 at the anterior end of the body in Trichomonas and some other flagellates, 

 the membrane divides from before backwards in these forms. In the 

 trypanosomes, however, the blepharoplast is situated at the posterior end 



of the flagellate, and the membrane 



divides from behind forwards. In 

 either case, the body itself divides 

 from before backwards after the mem- 

 brane has completed its division. 



Multiplication by binary fission 

 occurs also amongst the Opalinata 

 and C-iliata, but division is trans- 

 verse and not longitudinal, as in the 

 Mastigophora (Fig. 37). A ciliate 

 may develop a new cytostome at 

 some distance behind the first one, 

 and after division of both the macro- 

 nucleus and micronucleus the body 

 divides transversely or at right angles 

 to the longitudinal axis. It often 

 happens that, as a result of this 

 division, the character of the daughter 

 forms differs from the parent in the 

 relative size of the cytostome. As 

 the body of the new individual is 

 developed from the post-cytostomal 

 region of the parent, it follows that 

 the daughter forms will have a cyto- 

 stome which is relatively longer when 

 compared with the total length of the 

 body. In Paramecium the cytostome 

 of the parent takes up a position at 

 the centre of the body, and is divided 

 into two cytostomes of equal or unequal length, after which the body 

 divides transversely between the two. 



Binary fission, when it occurs amongst the Rhizopoda, Mastigophora, 

 or Ciliophora, usually gives rise to individuals which are roughly equal in 

 size; but not infrequently, as, for instance, in Trypanosoma lewisi, a large 

 trypanosome will divide in such a manner as to give rise to one large form 

 and one which is very much smaller (Fig. 197, 5). The process is repeated 



Fig. 37. — Binary Fission of Para- 

 mecium aurelia ( x ca. 500). (After 

 Lang, 1901.) 



1 and 4, New contractile vacuole; 2 and 6, 

 dividing macronucleus ; 3 and 5, anterior 

 and posterior contractile vacuoles, which 

 will become the posterior vacuoles of the 

 daughter forms ; 7. new cytostome formed 

 as bud from original cytostome; 8 and 10, 

 mitotic division of two micronuclei. 



