238 



BIOLOGY OF THE PROTOZOA 



or like a tadpole in form, but later is more block-like or rounded. 

 During growth the nuclei multiply, and the body when full-grown 

 approaches a spherical form, and becomes divided up within its 

 own periplast into a number of daughter individuals, which writhe 

 and twist over each other like a bunch of eels within the thin 



Fig. 118. — Trypanosoma lewisi. Cycle in the rat-flea Ceralophyllus fasciatus. 

 1, 2, ))lood trypauosomes entering the .stomach; 3,4, entering epithehal celLs; 6 — 10, 

 intracellular somatella-formation ; 11, 12, adult tryijanosomes leaving cell; A^, young 

 trypanosomes repeating intracellular phase; C, Crithidial forms; H, haptomonads 

 reproducing by division. (After Minchin and Thompson.) 



envelope enclosing them (Fig. 118, 11). When this stage is reached, 

 the flagellum, which hitherto had l>een performing acti\'e movements 

 and causing the organism to rotate irregularl\' within the cell, 

 disappears altogether, and the metabolic movements cease; the 

 body becomes almost perfectly spherical, and consists of the peri- 

 plast envelope within which a number of daughter trypanosomes 



