376 Trypanosoma lewisi 
the nucleus is seen dividing without any direct relation to the 
blepharoplast. 
The resemblance of these forms with Crithidiae and round forms 
from the flea’s gut is indeed very striking and we do not hesitate to 
consider these stages of the development of T. lewisi in the flea as 
merely natural culture forms. This cannot be said however of the 
“ small trypanosomes,” they have never been observed in the culture 
either by us or by any other authors. 
Figs. 1—3. Thick and slender crithidiae. G. Figs. 4—8. Dividing round forms. G. 
Comparison with species of Grithidia described in different fleas. 
Flagellates in fleas have been described by Swingle, Balfour and 
MacKinnon. Swingle considers the flagellates, found in the gut of 
fleas fed on rats infected with T. lewisi, as developmental stages of the 
latter flagellates. We gather from his description that he found small 
oval and round forms, but he did not trace out the whole cycle. 
Balfour found small, large oval, and round forms in Pulex cleopatrae, 
perhaps also small trypanosomes, but this point is not clear, because 
his preparations were obviously not well stained and so no flagella are 
to be seen. 
