TRYPANOSOMA LEWISI 471 



the cell, so that a reduction in size seems to have taken place. The pear- 

 shaped body now grows in size, while the kinetoplast and nucleus multij)ly 

 by repeated divisions. New fiagella are formed from axonemes which 

 develop from the daughter kinetoplasts, while the original flagellum still 

 persists with its axoneme attached to one of the kinetoplasts. The bodies 

 produced were described by Minchin and Thompson as " spheres." They 

 may be spherical, with the fiagella arranged irregularly about the surface 

 of the " sphere," or the flagellar end of the original parasite may still 

 survive, while the new fiagella are arranged parallel to it, forming a tuft 

 of bunched fiagella. In the living condition the " spheres " are in constant 

 motion. The number of nuclei and kinetoplasts produced is generally 

 eight to ten, but there may be as many as fourteen. The diameter of 

 the fully-developed "sphere" is 8 to 10 microns, and it finally divides 

 into a number of trypanosomes which bear a striking resemblance to the 

 original forms taken up from the rat's blood. The invaded cell is often 

 reduced to a mere membrane enclosing the activ'ely moving trypanosomes. 

 It is suggested that the periplast of the original trypanosome contributes 

 to the formation of this membrane. By rupture of the cell the trypano- 

 somes escape into the stomach of the flea (Fig. 200, 11-12). Sometimes 

 several " spheres " are developed in a single cell. The intracellular phase 

 of development occurs in all parts of the stomach, and, commencing about 

 six hours after the feed, it may cease as early as eighteen hours or persist 

 as long as four or five days. The trypanosomes which escape by rupture 

 of the cell may again enter other cells and repeat the process, but how 

 many times this may occur is not known. It is probably very variable. 



The next stage is the migration backwards of the trypanosomes to the 

 hind-gut and rectum (Fig. 200, 12). These forms, which have pointed 

 posterior ends and the kinetoplasts near but still posterior to the nuclei, 

 are evidently approaching the crithidia form. Minchin and Thompson 

 distinguish them as crithidiomorphic forms. Change in structure, which 

 may have commenced before the trypanosomes actually leave the stomach, 

 now takes place. This consists in a loss of activity, shortening of the body 

 with rounding of the posterior end, diminution in length of the flagellum, • 

 and transposition of the nucleus and kinetoplast to give the true crithidia 

 structure. Multiplication by fission of these crithidia forms takes place, and 

 there then ensues the established rectal phase, in which a great variety of 

 forms occurs (Fig. 200, 13-19). There are the typical short attached 

 (haptomonad) forms, the free-swimming (nectomonad) crithidia forms, and 

 finally the trypanosome forms. The small attached or haptomonad forms 

 are derived from the trypanosomes which migrated from the stomach, 

 and they give rise to the small infective trypanosomes (Figs. 197, 20-23, 

 and 200, 19, T). The attached forms multiply, as do also the free-swimming 



