^VIl] MODE OF DIVISION 



295 



number of individuals, and the most convenient way of pre- 

 senting the result of such a series of measurements is by means 

 of a Galtonian curve. With this graphic method it is possible 

 to detect whether the species is dimorphic or monomorphic, 

 and Bruce has shewn how it is possible to distinguish species 

 that have the same range of dimensions, e.g. T. brucei and 

 T. evansi. 



Mode of division. In the blood, the parasites multiply by 

 longitudinal fission, the details of which are essentially the same 

 in all species of trypanosomes. The first sign of division is 

 usually seen in the kinetonucleus, which seems to swell up, 

 resulting in the formation of an oval vesicle, throughout which 

 the chromatin is evenly distributed. The chromatin then 

 aggregates together in the form of a band lying across the middle 

 of the vesicle, which now becomes shghtly elongated. This 

 band then divides transversely and the two halves move apart, 

 one of them usually approaching the trophonucleus, and appar- 

 ently without any further changes, beyond the disappearance 

 of the vesicle, these two bands constitute the two daughter 

 kinetonuclei. The details of this process can only be observed 

 in those trypanosomes possessing a comparatively large 

 kinetonucleus and have not been followed in the case of those 

 species with excessively small ones. 



The end-bead, often with the basal part of the flagellum, 

 divides at the same time as the kinetonucleus. In some forms 

 the flagellum together with the undulating membrane divides 

 along a considerable part of its length, so that the new flagellum 

 is formed by splitting of the old one, whilst in other cases an 

 entirely new daughter flagellum develops from one of the daugh- 

 ter end-beads. 



The trophonucleus usually divides shortly after the division 

 of the kinetonucleus is complete. The central karyosome 

 divides, and the two halves move apart until they are situated 

 one at each pole of the nucleus, still remaining connected, 

 however, by a fine line. In some species the chromatin may 

 become arranged in the form of an equatorial plate, which then 

 splits transversely, each half moving up towards its respective 

 pole. In other species no equatorial plate is formed, but the 



