GENUS: TRYPANOSOMA 447 



So far reference lias been made only to the flagellates of the trypano- 

 some type, but it must be remembered that during the evolution of 

 trypanosomes, either in the vertebrate or invertebrate host, other types 

 appear — viz., crithidia, leptomonas, or leishmania forms. Thus, during 

 the early stages of infection of the rat with T. lewisi, a great variety of 

 forms may be found in the blood and organs, as also in its other host, 

 the flea (Fig. 197). During the development of T. gambiense and other 

 trypanosomes in tsetse flies, crithidia and other forms are found (Fig. 223). 

 T. cruzi, though appearing in the blood of the vertebrate as small flagel- 

 lates of the trypanosome type, reproduces intracellularly in the organs 

 as leishmania forms, and presents a still greater v^ariation in structure in 

 its invertebrate host, the reduviid bug, Triatotna tnegista (Figs. 206, 207, 

 209). It will thus be apparent that, before accurate knowledge of the 

 morphology of any trypanosome can be claimed, it is necessary to study 

 every stage of its development, both in the vertebrate and invertebrate 

 hosts. 



The cytoplasm of a trypanosome is usually clear and homogeneous or 

 finely alveolar, but there is frequently present a vacuole near the kineto- 

 plast. Sometimes the cytoplasm contains granules which are greenish 

 and refractile in life, and stain deeply purple with Romanowsky stains. 

 They are most frequently seen in the anterior region of the body, and 

 probably consist of volutin. According to Doflein (1916), the cytoplasm 

 of cultural forms of T. rotatorium of frogs may contain droplets of a fatty 

 substance. In some of the larger trypanosomes longitudinal markings 

 of the surface of the body have been described, and these are generally 

 regarded as contractile fibres or myonemes lying in the outer layer of 

 the cytoplasm (Fig. 28, B). There is no definite ectoplasm layer as 

 distinct from an endoplasm, but the surface of the body is limited by fine 

 membrane or periplast representing a concentration of the superficial 

 cytoplasm. The undulating membrane may be regarded as a lateral 

 extension of this limiting layer of denser cytoplasm. 



The nucleus is typically spherical, and consists of a nuclear mem- 

 brane enclosing a clear material at the centre of which lies a karyosome 

 (Fig. 156). It is situated usually at the centre of the flagellate. In some 

 cases, as in the posterior nuclear forms of T. brucei, it may lie near the 

 posterior end of the body and sometimes actually behind the kinetoplast 

 (Fig. 224). In others, as for instance, in T. lewisi, it has moved in the 

 reverse direction, and is typically found anterior to the central point of 

 the body (Fig. 197, 19). 



The kinetoplast, consisting of the blepharoplast and parabasal, as ex- 

 plained above (p. 329), lies at a short distance from the posterior end of 

 the body. It may actually be situated at the extreme posterior end, as in 



