300 



THE PROTOZOA 



forms with the flagellum very short, in some cases projecting 

 scarcely at all from the body at its pointed end. These forms are 

 found attached by means of their flagella, often in vast numbers, 

 to the wall of the rectum, sometimes also in the intestinal or pyloric 

 region ; they multiply by binary fission, and form a stock, as it were, 

 of the parasites, which persists for a long time in the flea probably, 

 under favourable conditions, for the whole life of the insect. Experi- 

 ments have shown that a flea once rendered infective to rats can 



FIG. 130. Trypanosoma lewisi: developmental phases from the stomach of the 

 rat-flea. 0, Ordinary form from the blood of the rat ; A F, intracellular 

 stages : A, a trypanosome curled on itself ; B, similar form in which the body 

 has become rounded ; C, multiplication beginning, division of kinetonucleus 

 and trophonucleus, daughter-flagellum growing out ; D, further stage three 

 nuclei of each kind, two short daughter-flagella, and a long parent-ilagellum 

 wrapped round the body ; E, six nuclei of each kind, five daughter- flagella, 

 parent- flagellum wrapped round the body ; F, eight nuclei of each kind, the 

 daughter-flagella running parallel with the parent-flagellum ; G, the type of 

 trypanosome resulting from the process of multiplication seen in the fore- 

 going figures ; this is the form which passes down the intestine into the rectum. 

 Magnified 2,000. 



N.B. The drawings in this figure and in Fig. 131 are made from prepara- 

 tions fixed wet with Schaudinn's fluid and stained with iron-haematoxylin ; 

 in such preparations the trypanosomes always appear appreciably smaller 

 than in films stained with the Romanowsky-stain (see Minchin, 479) ; con- 

 sequently these figures, though drawn to the same magnification as Figs. 11, 

 127, etc., are on a slightly smaller scale ; compare the trypanosome drawn in 

 with those in Figs. 11, A, and 127, A. 



remain so for at least three months, without being reinfected. 

 From the rectal stock trypaniform individuals arise by a process of 

 modification of the crithidial forms, in which the flagellum grows 

 in length, the anterior portion of the body becomes more drawn out, 

 the kinetonucleus migrates backwards behind the trophonucleus, 

 taking with it the origin of the flagellum, and an undulating mem- 



