1. The morphological and developmental anomalies of a pathogenic strain of Trypanosoma lewisi have been described to show the unusual character of the strain.
2. Especial attention is called to the spontaneous occurrence of ablepharoplastic forms of Trypanosoma lewisi.
3. It is pointed out that morphological anomalies were most pronounced in infections that showed unusual conditions of multiplication, and that such infections usually proved severe.
4. Finally, an appreciable correlation between the morphological and developmental characteristics and the virulence as manifested in these examples of infection with Trypanosoma lewisi has been suggested.