328 SYDNEY J. HIOKSON. 



Two individuals in proximity on a gill of Gammavus send 

 out simultaneously blunt lobe-like processes, which may be 

 called the conjugative processes. These meet but do not 

 completely fuse, a distinct membrane delimiting the process 

 of each individual throughout the conjugation. This mem- 

 brane does not prevent the fusion of the meganuclei nor of 

 the conjugative micronuclei in the latter stages, nor does it 

 prevent a certain amount of mixture of the cytoplasm of the 

 conjugating individuals. 



Stage A (PI. 17, fig. 2). — In the initial stage one or both the 

 meganuclei may exhibit pseudopodial processes indicating that 

 they have some power of amoeboid movement. The micro- 

 nuclei are a little but sometimes very little larger than they 

 were before conjugation. (In this respect, as in so many 

 others, there is considerable variability. The reader will 

 notice that the individuals drawn in fig. 1, in which the 

 coQJugative processes have not yet met the micronuclei, are 

 actually larger than they are in the individuals drawn in 

 fig. 2, which are actually conjugating.) 



Stage B (fig. 3). — The micronuclei increase considerably 

 in size during this stage, the chromatin being resolved into 

 a delicate skein. The meganuclei also increase in size, 

 become spindle-shaped, and show an arrangement of the 

 chromatin into roughly parallel lines. From this stage 

 onwards until Stage K (fig. 13) is reached, the meganuclei 

 increase in size without showing any material change in 

 structure ; and as the interest of the phenomena now centres 

 in the micronuclei, further reference to the behaviour of the 

 meganuclei will be for the present omitted. 



Stage C (figs. 4, 5). — When the micronuclei have i-eached 

 their full size the chromatin collects in the form of numerous 

 minute chi'omosomes in an equatorial plane. At the same 

 time extremely delicate, faintly staining threads (linin 

 threads) roughly parallel with one another, forming a tub- 

 shaped spindle, make their appearance. Neither in this nor 

 in any other stage of mitosis is there any sign of the 

 presence of centrosomes or similar bodies. I have found it 



