388 
Trypanosoma lewisi 
were to be seen. In the stained preparations of the posterior part of 
the midgut no trace of crithidiae or round forms could be found. There 
may or may not be some further development in bugs kept for a longer 
time, but our experiments show at least that there is some development 
and a survival for at least nine days. 
Summary. 
From the results of our experiments we may conclude that the 
development of T. lewisi outside the invertebrate host is not confined 
to one species or genus, but may take place at least in the rat louse 
and the rat flea and also (though perhaps more incompletely) in the 
bed-bug. We see further that development needs not always to be 
combined with longevity in the invertebrate host, but that sometimes 
life without development may be longer than with it (behaviour in the 
tick compared to that in the louse). 
When we compare the behaviour of T. lewisi in the four invertebrate 
hosts studied here, we see that the most complete cycle takes place in 
the flea, where forms are produced which are never found in cultures. 
In the louse the development may be truly described as a natural 
culture; in the bug, the development (as far as we could judge by our 
incomplete experiment) does not even produce all the cultural forms 
(only the crithidiae) and at last in the tick the trypanosomes do not 
develop at all but are only preserved for some time. 
We finish this paper by thanking Professor Nuttall for the liberal 
way in which he enabled us to carry out these experiments, and for the 
keen interest he always took in our work. 
REFERENCES. 
Baldrey (1909). Versucben und Beobachtungen liber die Entwickelung von Try¬ 
panosoma lewisi in Haematopinus spinulosus. Archiv f. Protistenkunde, vol. xv. 
Balfour (1906). Herpetomonas parasites in fleas. Journ. of Hygiene, vol. vi. 
Breinl aud Hindle (1910). Observations on the life-bistory of Trypanosoma 
lewisi in the rat louse ( Haematopinus spinulosus). Ann. of Trop. Med. and 
Parasitology, vol. ill. 
Chagas (1909). Pber eine neue Trypanosomiasis des Menschen. Studien liber 
Morphologie und Entwickelungscyclus des Schizotrypanum cruzi n. gen. n. sp. 
Erreger einer neuen Krankbeit des Menschen. Memorias do Instituto Oswaldo 
Cruz, vol. i. 
