CYTOLOGY 329 



(1924) has found that the nucleus of Leishmania donovani divides by 

 mitosis, as also that of Leptomonas fasciculata in cultures from the intestine 

 of Culex pipiens and Theobaldia annulata. It seems probable, therefore, 

 that the nucleus of the trypanosomes and the allied flagellates divides by 

 a form of mitosis, but the process is difficult to detect in such minute 

 objects, and can only be demonstrated by special staining. The ordinary 

 appearance at nuclear division is that of an elongating, deeply staining 

 karyosome which becomes constricted at the centre, as described above. 



An unusual type of nucleus has been described in the broad, leaf-like 

 forms of Trypanosoma rotatorium (Fig. 150, 38). It was first noted by 

 Franga and Athias (1906) in the trypanosome of Hyla, and then by Martin 

 (1907) in T. boueti. It was subsequently observed by other writers in 

 T. rotatorium of frogs (see p. 592). Instead of being spherical, the nucleus 

 is in the form of a long spindle, which is frequently curved. One end is 

 near the kinetoplast, while the other may be near the posterior extremity 

 of the flagellate. It has been shown by Noller (19136) that the large 

 trypanosomes of this type in the frog are the survivors of a tadpole 

 infection with flagellates of the more normal type, and are to be re- 

 garded as abnormal or overgrowth forms. The long drawn-out nucleus 

 may represent a division process which has been arrested at this stage. 



KINETOPLAST.— The kinetoplast consists of the blepharoplast and 

 parabasal body. The two appear to be united. This union has been 

 described as a system of fibres forming a cone, with the parabasal at its 

 base and the blepharoplast at the apex, or as a definite membrane enclosing 

 a space with the parabasal and blepharoplast at opposite poles. That 

 there is such a membrane is borne out by certain appearances seen in 

 degenerating trypanosomes, which the writer (1913a) studied in smears 

 made from heavily infected animals some hours after death. It was noted 

 that many trypanosomes were in various stages of disintegration, and 

 that frequently the cytoplasm had disappeared, leaving only the nucleus 

 and the kinetoplast, with the axoneme and flagellum still attached 

 (Fig. 157). The axoneme will be seen to terminate in the blepharoplast, 

 which appears to be lying on the surface of a membrane connecting 

 it with the parabasal. If the parabasal were a free and independent 

 structure, it would be expected that in disintegration or cytolysis the 

 parabasals would not remain united, as they appear to do. Dividing or 

 already divided blepharoplasts and parabasals still show this connection 

 with one another and with the axoneme of the flagellum. It is interesting 

 to note that in these degenerating forms there is no evidence of a fibre 

 connecting the kinetoplast with the karyosome of the nucleus, as several 

 observers have described. 



The first indications of division are seen in the kinetoplast. The 



