90 mxrcLEATK cells i\ Tissrr: cilti'res. 



a 7-day chick licart in glycosaline with autogenous embryonic extract, the culture 

 being 19 hours old when the observation commenced. 



At 11'' 55'" a. m., when the observation began, the nucleus (fig. 00) was seen 

 to be com])()sed of two portions, ai)pi-oximately ecjual, separated by what api)eared 

 to be a single membrane, but what really rejjre.sents, as has been shown, the api)osed 

 areas of nuclear membrane of the two portions. This double partition was seen, 

 by focusing at different levels, to be a plane surface. The first three drawings show 

 roughh' the ajipearance of such a double nucleus during life. The i)arts are of 

 al)out the same size and each at first contains a single nucleolus. These latter 

 undergo obvious changes in size, shajje, and number. There is a single centro- 

 sphere (r). Vai globules are numerous, and the mitochondria are thread-like and 

 ])lainly visil)le, and show their characteristic movement. 



The nucleus remained in much the same condition, undergoing minor changes 

 in outline, for about 2 hours, when, at 1'' 50'" p. m. (63) the division between the 

 nuclear i^arts was seen to become less clearly defined at one side and, gradually, 

 refractive material from the nucleus accumulated in this equatorial plane until, 

 at 5'' 05"' )). m. (65), there was a distinct refractive mass in this region, which was 

 evidently chromatin. Hoon the entire cell began to contract, to become rounded, 

 and to draw in its processes; the nuclear outline became indistinct, the i)osition 

 of the nucleus being rejjresented by a clear space surrounded by a ring of fat globules 

 and mitochondria (66). By focusing up and down it is seen that the cell is much 

 thicker than before — in fact, it is almost spherical, the mitochondria and particles 

 of fat forming a hollow globe which incloses the imclear space. The portions of 

 the twin nucleus have (juite evidently fused and (from our knowledge of mitosis) 

 it is plain that the cell is now in the prophase. A sijireme, however, could not be 

 made out. The refractive material which had been seen between the nuclear 

 portions has become indistinct. This stage was seen at 6 p. m. 



If we could see the cell represented in 65 in the fixed and stained condition we 

 would tloubtless find something like figure 22; here the spireme is forming in a 

 binucleate cell and the nucleoli are becoming smaller and are breaking up. It is 

 evidently composed of two such nuclei as are seen in hgure 14, an early prophase in 

 a mononucleate cell. The accumulated chromatin in the i)lane of contact of the 

 two nuclear portions is clearly evident; this is ol)viousIy not the equatorial plate 

 of mitosis. The nuclear membrane has almost disappeared, but the clu-omatic 

 material is somewhat mor(> concentrated about the ])eriiihery. 



Figure 23 evidently represents a somewliat later stage of spireme formation in 

 a double nucleus. Here the skein is well marked and the nuclear membrane has 

 completely disajjpeared. These figures bear a striking resemblance to figure 6 of 

 Rubaschkin (1905), in which he shows a spireme in a double nucleus. 



The stage represented in 66, if fixed and stained, would probably resemble 

 figure 19, drawn from a mononucleate cell in the late prophase. From this point 

 on the behavior of the combined double nucleus is identical with that of an ordinary 

 single nucleus. 



As the cell was watched it was seen that a line, refractive in character, formed 

 across its equator; this Une, represented in 67, was somewhat irregular in outline, 

 its borders being serrated. It did not remain unchanged, l)ut on the contrary 



