TRYPANOSOMA LEWISI 



9 1 



still remaining attached for a time. The cytoplasm then divides into 

 daughter trypanosomes which are contained within an envelope, 

 formed by the periplast of the parent parasite. Inside the periplast 

 envelope are a number of daughter trypanosomes " wriggling very 

 actively ; the envelope becomes more and more tense, and finally 

 bursts with explosive suddenness, setting free the flagellates, usually 

 about eight in number, within the host-cell " (fig. 38, F). The daughter 

 forms escaping from the host cell into the stomach lumen of the flea 

 are fully formed, long trypanosomes. 



FIG. 38. Trypanosoma lewisi. Developmental stages from stomach of rat flea. O, 

 ordinary blood type ; A F, stages occurring in gut-epithelium of flea, when the trypanosome 

 becomes rounded and undergoes multiplication, forming in F eight daughter trypanosomes ; 

 G, type of trypanosome resulting from such division which passes back to the rectum. 

 X 2,000. (After Minchin.) 



The trypanosomes (fig. 38, G) pass into the flea's rectum. The 

 next phase is a crithidial one. The parasites become pear-shaped, 

 in which the blepharoplast (kinetic nucleus) has travelled anteriorly 

 past the nucleus towards the flagellum (fig. 39). The crithidial forms 

 attach themselves to the wall of the rectum, and multiply by binary 

 fission (fig. 39, D). A stock of parasites is thus formed which, 

 according to Minchin and Thomson, " persist for a long time in 

 the flea probably under favourable conditions, for the whole life 

 of the insect " (fig. 39, A I). 



From the crithidial forms of the rectum, according to Minchin, 

 small infective trypanosomes arise by modification morphologically 

 (fig. 39, ] M). The flagellum grows longer and draws out more the 

 anterior part of the body, the blepharoplast migrates posteriorly, 

 behind the nucleus, and carries with it the flagellar origin. These 

 trypanosomes are small, but broad arid stumpy (fig. 39, N), and can 



