158 Mr. C. C. Dobell. Observations on the [Nov. 19, 



A micromerozoite, such as that just described, may increase in size and 

 become a microgametocyte (text-fig. 2 (1) ). It then becomes attached to 

 a macrogametocyte in the usual manner. During its transformation into 

 a microgametocyte, the karyosome travels to the centre of the nucleus, 

 and is apparently reinforced by the nuclear chromatin. A part of this 

 latter, however, is usually to be found lying free in the clear nucleus in the 

 form of granules. 



The next step towards the formation of the microgametes consists in 

 a dispersal of the karyosome and the formation of a chromatic network in 

 the nucleus. This is shown in (2) text-fig. 2, and may take place before 

 association occurs. Further breaking up* of the karyosome now ensues — 

 provided that association has taken place — the chromatin particles invading 

 the cytoplasm and there forming a chromidialf net (3). When the 

 karyosome is completely broken up, and the outline of the nucleus has 

 completely disappeared, the microgametocyte is seen to contain a chromidial 

 net completely filling it from end to end (4). The foregoing stages (1 to 4) 

 may be conveniently termed the analytic phase. Those which follow 

 constitute what I may call the synthetic phase, in which four new nuclei 

 are built up from the chromatic elements of the old nucleus. Synthesis 

 begins with the gathering up of the chromidial net into a more or less 

 rounded mass (5) which soon becomes constricted in the middle, giving rise 

 to a dumb-bell shaped reticulum (6). If deeply stained, it has the appear- 

 ance of a dividing nucleus.^ The ends of the dumb-bell now extend 

 transversely, and the chromatin becomes localised at the four poles so 

 formed (7). At the same time, the intermediate portion becomes diffuse ; 

 it finally breaks up, undergoes degeneration, and is left behind — with a 

 small quantity of pigment — in the residuum of the microgametocyte 

 when the microgametes forsake it. 



Four special points, we have seen, have now become centres for the 

 aggregation of chromatin. Chromatin continues to travel to each point, and 

 at first arranges itself in the form of a loose net. The net then resolves 



* The exact manner in which the breaking up of the karyosome takes place is unknown 

 to me. I have never been able to watch the process in the living animal. That breaking 

 up does occur is inferred from the fact that the karyosome becomes smaller and smaller, 

 whilst the chromatin granules increase in number. 



+ See, further, under "Chromidia," next page. 



I I should like to mention here the fact that published figures purporting to show two 

 nuclei in the microgametocyte really show what I believe to be the stage just described. 

 All the figures given by Siedlecki show two " nuclei " connected together — in no case are 

 they completely separate. Siedlecki's "corpuscule intermediate " is, I believe, a more 

 deeply stained portion of the intervening network. 



