Two forms of the parasite (fig. 33, _6_, _7_) are described in the human blood. In one free form there is a large egg-shaped blepharoplast and the posterior (aflagellar) end of the parasite is drawn out. The blepharoplast (kinetic nucleus) may have a chromatin appendage. The nucleus is oval or band-like, containing a karyosome. The flagellum, starting close to the blepharoplast or its appendage, has a free portion of variable length. The other free form in the blood has a more or less round, terminal blepharoplast, smaller than in the first form, without a chromatin appendage as a rule. The body of this second form is decidedly broader than that of the first mentioned. [Illustration: FIG. 33.--_Trypanosoma cruzi_. Schizogony. _1_, merozoite in red blood corpuscle; _2_, parasite totally enclosed in red cell, no flagellum or undulating membrane; _3_-_5_, parasites partially enclosed in red cell; _6_, _7_, parasites in human blood; _8_-_11_, parasites in lungs of the monkey, _Callithrix_; _12_, _13_, initial forms of schizogony; _14_, _15_, schizogony in the lungs of _Callithrix_. (After Chagas.)] The dimorphism has been interpreted sexually, the first mentioned forms being termed males, the second ones females. The correctness of this interpretation is very doubtful. No sign of longitudinal division was ever seen in the peripheral blood or in the internal organs. The “endocorpuscular” forms may be completely or partially enclosed in the red cell or only attached thereto (fig. 33, _1_-_5_). At the beginning of infection the endocorpuscular forms are the more numerous. Some authorities, however, doubt these stages. _Life-history in the Vertebrate Host._--Chagas found fluctuations in the number of the parasites in the peripheral blood. He believes the increase of the parasites to be periodic. The investigations of Chagas and of Hartmann have revealed two types of multiplication which take place in the internal organs of the vertebrate host.