384 Trypanosoma lewisi 
palely, and at last nothing of it is to be seen but some irregular 
chromatic filaments, sometimes connected with extranuclear granules 
(Fig. 1); the blepharoplast also disappears. 
We never were able to see anything beyond these stages, nor did the 
other authors who studied this subject. We utterly failed to find any 
form which could be identified with the “ small trypanosome ” forms in 
the flea. 
Diagram XIX. Degenerative stages. 
When comparing these types with the cultural forms, we see that 
there is here a perfect resemblance, all the flagellated forms found in 
the gut of the louse may be found in the culture (cf. Diagrams XYI— 
XIX with Diagram XII). We think therefore that the development in 
the gut is a mere natural culture which lasts only for a short time, so 
long as the blood remains in the gut; but there is no real adaptation 
to the natural conditions of the gut. Perhaps the non-appearance of 
the small trypanosomes has something to do with this phenomenon. 
During the first two days of the infection many degenerative forms 
are to be found, which are identical with those found in the flea’s gut, 
so we abstain from describing them. 
No signs of sexual processes were observed. The thick and slender 
crithidiae, described during the first two days of development, which 
might be considered as sexually differentiated forms, cannot be regarded 
as such owing to the fact that subsequent observation did not establish 
the occurrence of conjugation or any other sexual process. 
We never could find any trace of development in the coelom as 
Baldrey and Prowazek did. 
5. Behaviour of T. lewisi in the gut of Ornithodoros moubata. 
After our positive results in trying to find developmental stages of 
T. lewisi in the gut of the flea and the louse, we tried to answer the 
question if there may be development in some other blood-sucking 
Arthropods. We chose a tick (Ornithodoros moubata) and the bed bug 
(Acanthia lectularia ), because they suck large quantities of blood which 
