216 THE HAEMOFLAGELLATES 



shown (Fig. 12). An additional feature of interest is the presence 

 of a well-developed axial spindle, still connecting the two tropho- 

 nuclei (which have divided last), and ending in a granule inside 

 each, which is doubtless the trophonuclear centrosome. In other 

 cases (e.g. T. remaki, Trypanoplasma borreli, Trypanopliis) as well, a 

 large, distinct granule has been described in the centre of the nucleus, 

 which very probably represents the trophonuclear centrosome 

 (karyocentrosome). To sum up, the above facts leave little reason to 

 doubt (a) that the kinetonucleus of a Trypanosome is not merely 

 an extranuclear centrosome, 1 but a true nucleus, homologous with 

 and equivalent to the trophonucleus, the two being specialised for 

 different functions ; and (b), that distinct centrosomes are associated 

 with both nuclei, the trophonucleus possess- 

 ing an intranuclear one, while in connection 

 with the kinetonucleus there is an extra- 

 nuclear one (at the base of the flagellum) 

 and perhaps also an intranuclear one (accord- 

 ing to Schaudinn). 



Both nuclei vary greatly with regard 

 to their position in the body, in different 

 forms, as will be seen on comparing the 

 figures given. As a rule, the trophonucleus 

 P IG . 12. lies somewhere near the middle of the body, 



Trypanosorna grayi, dividing, and the kinetonucleus near the aflagellar 

 nlnTdrlwtfti So^SS end, being farther from it in proportion as 

 somic granules are seen one the extremity is tapering. In some cases, 



above each kinetonucleus. ' a . . . ' 



however, at all events during certain periods 



of life, the two nuclei lie close together centrally, at times being 

 actually in contact (cf. T. inopinatum, Fig. 8, C ; T. " iransvaaliense," 

 Fig. 33 ; T. rotatorium, Fig. 8, B; and T. lewisi, young forms, Fig. 

 21, E). The trophonucleus is generally ovoid in shape, the longer 

 axis being longitudinal, but in the Trypanosome described by 

 Button and Todd from Senegambian birds, and also in T. hannae, 

 the long axis is transverse to that of the body (Figs. 7, G; 35). 

 As regards its minute structure, the trophonucleus appears generally 

 to consist of an aggregation of chromatin grains embedded in a 

 plastin-like matrix. No mention is usually made of a nuclear 

 membrane or reticulum. In his account of Trypcmoplasma borreli, 

 it may be noted, Le"ger (49) has described eight dumb-bell-shaped 

 chromosomes. An unusual appearance of the trophonucleus has 

 been observed in one or two instances (T. brucii, Stuhlmann and 

 Miss Kobertson ; T. raiae, in the leech, Miss Robertson). In these, 



1 Salvin-Moore and Breinl, in their account of the " cytology of the Trypanosomes " 

 (Ann. Trap. Med., Liverpool, 1907), continue so to regard this organella, in spite of 

 all the evidence to the contrary, much of which (e.g. that furnished by Trypanoplasma) 

 they entirely overlook. 



