Page:Tropical Diseases.djvu/987

Rh flagellum is free from the body and devoid of an undulating membrane. Several species have been described from human fæces, and one, P. cruzi, is considered to be the cause of a diarrhœa in China.

Suborder 4.—The Hæmoflagellata and allied forms are an important suborder of the Protomonadina, and under this term are grouped a number of forms having a characteristic but not invariable parasitic habitat in the blood of vertebrates and in the digestive tract of invertebrates.

The group comprises a number of heterogeneous forms conveniently grouped together, their chief morphological feature being the possession of two nuclei, a tropho- and a kinetonucleus (blepharoplast). For this reason they were included by Hartmann as a distinct order of the Flagellata and termed the "binucleata."

The following five genera represent the more important types: (1) Trypanosoma, (2) Trypanoplasma, (3) Crithidia, (4) Herpetomonas, (5) Leishmania.



1. .—The structure of the trypanosome body is of a uniform type, though subject to variation in minor details. The body is long and sinuous; the anterior end tapers gradually to a narrow point, while the posterior end generally terminates more bluntly.

The principal nucleus (trophonucleus) is situated centrally; the kinetonucleus is usually placed posterior to the nucleus, but is sometimes closely approximated to it. Certain exceptions to this rule are known, namely, the recently described T. rhodesiense (p. 185), and some multiplicative forms of T. lewisi. The flagellum arises from a centriole (blepharoplast) closely connected with the kinetonucleus, and passes forwards as the margin of the undulating membrane; in some cases it may end with the undulating membrane at the anterior extremity of the body, but more usually it projects forwards as a free lash. The arrangement of the centriole and kinetonucleus varies; sometimes the former is lodged within the latter, sometimes connected with it by a delicate rhizoplast. In one species,