This organism was discovered in the blood of a sloth (_Cholœpus didactylus_), in South America (French Guiana).[107] It possesses special interest, in that the best known form of the organism is endoglobular, inhabiting the erythrocytes of the sloth. A free trypanosome in the same animal was considered to be different from the endoglobular form, which was somewhat like a peg-top, and possessed a short flagellum. Darling[108] (November, 1914) has seen the organism in Panama. He describes free crithidial forms in shed blood, but not in the blood-stream of the sloth. [107] _C. R. Soc. Biol._, lxv, p. 581. [108] _Journ. Med. Research_, xxxi, p. 195. *Trypanosoma boylei*, Lafont, 1912. This is a parasite of the Reduviid bug, _Conorhinus rubrofasciatus_. The insect attacks man in Mauritius, Réunion and other places. Lafont infected rats and mice by intraperitoneal injection with the gut-contents of infected bugs. Trypanosomes appeared in the mice. Other flagellate types were assumed by the parasites in the bug. MONOMORPHIC TRYPANOSOMES. A number of trypanosomes, characterized by relative uniformity in size and structure, may be considered under this heading. They occur in cattle, sheep, goats and horses in Africa, especially West Africa. Morphologically, they are characterized by the posterior (aflagellar) part of the body being swollen, while the anterior part narrows. The nucleus is central and situated at the commencement of the narrowing of the body. The blepharoplast is almost terminal, the undulating membrane is narrow and not markedly folded, so that the flagellar border lies close to or along the body. The flagellum may or may not possess a free portion. Some recent workers have considered that _T. brucei_ (Zululand strain) and _T. evansi_ are also monomorphic, but they do not exhibit the general characteristics outlined above. _T. brucei_ and _T. evansi_ have already been considered separately. The monomorphic trypanosomes, as defined above, include:-- *Trypanosoma vivax*, Ziemann, 1905. This trypanosome[109] occurs in cattle, sheep and goats, and was first found in the Cameroons. It is fatal to cattle. Equines are also affected. Antelopes are the possible reservoirs of the trypanosome. It is probably transmitted by _Glossina palpalis_ and other tsetse flies. Its movement is very active. It possesses a free flagellum (fig. 45) and it averages 23 µ to 24 µ in length. _T. cazalboui_ (Laveran, 1906)--the causal agent of “souma” in bovines and equines in the French Sudan--is probably synonymous with _T. vivax_. [109] See Bruce and colleagues (1910), _Proc. Roy. Soc._, B, lxxxiii, p. 15. [Illustration: FIG. 45.--_Trypanosoma vivax_. × 2,000. (Original. From preparation by Fantham.)] *Trypanosoma capræ* (Kleine, 1910) is allied, but is somewhat broader and more massive. It was found in goats in Tanganyika. *Trypanosoma congolense*, Broden, 1904.