461 
period at which the black line is formed. At this period the extra- 
nuclear centrosome develops a bridge, as it were, and connects itself 
for the time with the nucleus. It may be assumed that during this 
period some substance from the extra-nuclear centrosome passes into 
the nucleus. Anyhow, after this has taken place the remains of the 
extra-nuclear centrosome are very shortly cast away, together with the 
greater part of the protoplasm forming the rest of the cell, and the 
old flagellum. 
Thus, if we consider the nuclear apparatus in the latent body as a 
whole, this would seem to be divided into two parts during the 
development of the trypanosome. After the formation of the cell is 
complete, these two structures, the nucleus and the intra-nuclear 
centrosome, remain in the same state, and multiply independently 
into similarly distinct bodies contained in the cells produced by all 
the longitudinal fissions. In other words, there arises from a nucleus 
A, two new structures, B and C, both of which differ from A. B and 
C multiply independently as the animals divide, but at a subsequent 
stage a portion of each B unites again with the C in all the cells, and 
the condition of the organism immediately reverts to A once more. 
We have thus, after the formation of the latent bodies, 
an unequal division of the nuclear apparatus of the latent body, 
so as to form two different sets of structures, the nucleus with one 
centrosome, and the other centrosome by itself. Each of these then 
multiplies indefinitely in number. In individual cells these structures 
subsequently unite temporarily, and later the nucleus characteristic of 
the latent body is produced once again. In other words, dissimilar 
structures are formed from a nucleus by division, both derivatives 
multiply by division, and after a time unite in pairs, and the first type 
of structure is again produced. There is in this process, when 
contemplated from the present standpoint, an obvious similarity to 
the two forms of sexual elements in the higher animals and plants , to 
two sorts of gametic nuclei, or to a sexual dimorphism. A 
dimorphism in the trypanosomes which is in like manner followed by 
a reunion, or conjugation between the dissimilar elements, and 
succeeded by a reversion to the conditions obtaining before the 
dimorphism was produced. 
The procedure in the case of the trypanosome nuclear apparatus 
differs, however, from that of apparently all other known organisms 
DD 
