0. Strickland 
89 
8. Crithidia ctenophthalmi was found in 9 Gtenophthalmus agyrtes. 
9. About 370 lice and 75 fleas were examined but no evidence was 
obtained of developmental changes of T. lewisi in either fleas or lice. 
Concluding remarks. 
Professor Nuttall (190S) has proved that the transmission of rat 
trypanosomiasis can be easily brought about by fleas, and much less 
readily by lice. Consequently the flea is certainly the usual carrier of 
the trypanosome. The question arises whether this transmission depends 
upon these arthropods being true hosts of the trypanosomes. The 
observations recorded above afford no support to the view that the fleas 
and lice are true hosts of the parasite, nor that any sexual process of 
development of T. lewisi occurs in the arthropods. 
Prowazek (1905) may have been misled by natural parasites of the 
louse, having no connection with T. lewisi , when he described the sup¬ 
posed sexual process of this trypanosome. If he saw a real stage in its 
development, we can say it must be rare, for we have never seen it. 
On the other hand, it is not easy to understand the mechanism of 
infection. Jordan and Rothschild (1908) say 7 that the proventriculus of 
the flea is designed to prevent regurgitation of stomach contents during 
feeding. Therefore it seems that infection by fleas is not effected by 
regurgitation of gut-contents. Possibly infection is effected by the 
inoculation of the minute drop of blood, which probably remains in the 
mouth-parts and around the opening of the salivary ducts in the 
pharynx of the flea. 
With regard to the louse, it appears that the trypanosomes persist 
for a lengthy period in the gut. The louse being a constant feeder, it is 
almost certain that trypanosomes ingested at one meal would survive 
until the next. If then, as Prowazek (1905) asserts is the case, lice 
regurgitate the gut-contents, this seems a probable mode of infection. 
REFERENCES. 
Jordan, K., and Rothschild, N. C. (iii. 1908). Revision of the non-combed eyed 
Siphonaptera. Parasitology , i, No. 1. 
MacNeal, W. J. (xii. 1904). The life history of Trypanosoma lewisi and brucei. 
Journ. Infect. Diseases , I, pp. 517—543. 
Nuttall, G. H. F. (xii. 1908). The transmission of Trypanosoma lewisi by fleas 
and lice. Parasitology, I, p. 296. 
