532 Messrs Strickland and Swelle^igrebel, The development 



Twelve hours after feeding on the infected rat, T. lewisi may- 

 be found unaltered in the midgut, after 24 hours the blepharoplast 

 leaves its terminal position and approaches the nucleus. The 

 hind-end of the flagellate becomes larger so that the trypanosome 

 appears club-shaped. The nucleus now wanders to the hind-end 

 of the flagellate, and consequently the distance between the 

 blepharoplast and nucleus diminishes gradually, and at a later 

 stage the two pass each other so that the blepharoplast is situated 

 in front of the nucleus, the trypanosome having now a Crithidia 

 facies. This change is accomplished in the midgut in 1| days. 

 The club-shape is now very well marked and the front-end of the 

 flagellate becomes thinner and thinner, the flagellum often staining 

 with difficulty. At last the flagellar end of the parasite atrophies, 

 and the trypanosome is now metamorphosed into an oval-shaped 

 cell, with a short flagellum, the blepharoplast being situated at 

 the side or in front of the nucleus. These " large oval forms," as 

 we may call them, pass into the anterior part of the hindgut, 

 and are to be found there after 3^ days in rosettes. During the 

 following days the large oval forms become rounded, giving rise to 

 the so-called " round forms," which begin to divide actively after 

 5 — 6 days. This development is first to be observed in the flea's 

 rectum but afterwards also in the hindgut. We never observed 

 any indication of multiple division, but the parasites arising from 

 the repeated binary division of the round forms hold together with 

 the front-ends, so that rosettes are formed. These rosettes are 

 composed of " little oval forms " with short flagella, the blepharo- 

 plast being situated just in front of the nucleus. Gradually these 

 become more elongated, the flagellum grows out further, and 

 the blepharoplast passing the nucleus comes to lie in the posterior 

 end of the cell. Since the flagellum follows the blepharoplast, the 

 result is the formation of an undulating membrane. The parasite 

 has now recovered the aspect of a small trypanosome with a 

 particularly large blepharoplast, situated at the extreme posterior 

 end. These forms begin to appear after 7 days but are abundant 

 after 8 — 10 days and remain so for an indefinite time, probably 

 till the host's death. 



All these different types of parasites — little ovals, intermediate 

 Crithidiae and small trypanosomes — may divide, so that prepara- 

 tions made during the last stage of infection exhibit a great 

 variety of forms. The small trypanosomes and the Crithidiae 

 from which they originate occur in two well-marked types : a 

 slender one and a stout, but united by intermediate, forms. We 

 do not know if this is to be considered as a sexual differentiation, 

 but we have never seen any sign of conjugation. 



Not being able to find any further stage of development 

 beyond that of "small trypanosomes," either in our series or in 



