204 
Tiiat such a progressive development in the case of each individual 
really represents the course of the cycle in the blood, receives complete 
confirmation from the study of the various morphological changes 
which take place at the successive periods of the cycle ; for these 
changes, as we shall see, correspond closely to the analogous changes 
which occur during the development of T. cquiperdum and 
2 . gambiense, that is to say, in forms where the successive stages are 
passed through approximately simultaneously by the majority of the 
parasites during the course of infection. 
The study of the morphology of 2 '. IchJtsi may perhaps most 
simply be illustrated by taking in the first place examples such as 
those represented in fig. i. In this condition the cell is long and 
pointed at both ends. Tire extra-nuclear centrosome, which is laige, 
lies at a considerable distance from the pointed extremity of the cell 
file extra-nuclear centrosome stains very deeply with many forms of 
coloration, and can be seen during life as a highly refractive body- 
In various stained preparations tlie extra-nuclear centrosome appears 
to be always related to a vacuole, or space in the surrounding 
cytoplasm, and the flagellum may present various appearances in 
relation both to the vacuole and the extra-nuclear centrosome. The 
flagellum, which is a long stainable band, extends in a curved course 
over the whole length of the body, and projects at the opposite end 
as a whip-lash. It is enclosed in a thin expansion of the cytoplasm, 
forming the so-called undulating membrane. The flagellum generally 
ends in a small body, or bead, near the extra-nuclear centrosome (fig.i}i 
but this is not always the case, for at times it certainly appears to run 
directly on to the extra-nuclear centrosome. When the flagellum is 
detached from the latter body, there can frequently be seen passing 
from tile bead or thickening at the end of tlie flagellum, fine unstained 
strands wliich connect the bead with the extra-nuclear centrosome. 
The bead upon the end of the flagellum corresponds closely m 
appearance to tlie similar beads which are often found at the ends of 
the flagella among metazoan gametes, and such beads are in like 
manner often connected with the centrosomes by fine slightly staining 
strands. It would thus appear that so far as these structures among 
the trypanosomes can be directly homologised, the flagellum and its 
en ead, together with the extra-nuclear centrosome, would 
correspond to the flagellum, bead, and centrosomes of many forms of 
