226 
forms of trypanosomes? The analogy of malaria in man and of 
protozoa in cultures suggests an answer— chronic infections.* 
( 3 ) Young malarial parasites (ring forms) divide by direct division ; 
a cycle of sporulation exists, yet there is also a sexual cycle. 
(4) These facts need only signify that the parasites were not, at 
the moment of inoculation, in a state favourable to cultivation or to 
the production of infection in a vertebrate host. 
Coccidium schubergi is parasitic in a centipede. Infection takes place by the 
digestive canal. If an infected centipede be eaten by another, infection may be 
conveyed by almost every stage of the parasite ingested. The immature gameto- 
cytes, however, are unable to infect ; although they are in their normal host their 
surroundings are unsuited to their further development. They consequently die. 
In cover-slip preparations the malarial gametocyte is fertilized, 
development goes but little further; the surroundings are not 
favourable. Why should the sexual cycle of a trypanosome necessarily 
occur in the same medium as its asexual one ? Crescents, males at 
least, adult malarial parasites, if left in man degenerate ; the young 
parasites die in the mosquito. The surroundings suited to one form 
are not to the other. Why should the hypothetical sexual form of a 
trypanosome develop equally well in either invertebrate or vertebrate 
host ? 
The cited arguments proffered against the existence of a sexual 
cycle of trypanosomes in tsetse flies are contradicted by these known 
acts. What are the arguments in favour of it ? They are briefly = — 
(0 The analogy of other protozoa. 
(2) The occurrence of parasites possessing sexual characteristics m 
ood of infected animalsf (compare Trypanosoma dimorphon)■ 
( 3 ) Prowazek’s observations on the development of Trypanosoma 
tewisi in the rat. 22 
trvnan KocllS . mcorn P let e observations on the development of cattle 
trypanosomes in Glossina* 
'Pposedly sexual forms, somewhat similar to some of those 
made on 
somes they ingested onlvltp^f Glossinae only became in 
animal m whose blood the n ° P - ed lf their feed had been 
f The acknowled paras,tes were scanty, 
tneasure on a recognition'of* nature of these forms of course depends ii 
een re P°rted in nianv trvnan east a P art of Schaudinn’s work (21). The 
• 1 os °mes by many independent observers. 
