260 Robert Wilhelm Hegner. 



chromatin partially arranged in an equatorial plate. An enlarged 

 \dew of the two nuclei which lie nearest the posterior pole (Fig. 18) 

 shows that each is surrounded by an auKEboid mass of cytoplasm 

 with many fine pseudopodia-like processes extending outward in all 

 directions, finally becoming lost among the yolk-globules. The 

 nuclear membrane of each nucleus has disappeared, but its former 

 position is clearly marked by the difference in density between the 

 cytoplasm and the nuclear sap ; a fusion of these two substances 

 has not yet taken place. 'No nucleolus is visible. 



After this division is completed, the daughter nuclei are closer 

 together and nearer the surface of the egg (Fig, 7, a). The two 

 nuclei with their accompanying cytoplasm, which now lie closest 

 to the posterior pole (Fig. 19), have finally come in contact by means 

 of their pseudopodia, with the ^'Keimhautblastem." These two nuclei 

 are in a resting condition; their chromatin is evenly distributed 

 throughout, the chromomeres lying in a linin reticulum singly or 

 in groups of from two to six or more. One small nucleolus is present. 

 All the other nuclei in the egg are similar in appearance at this time, 

 and no differences in size or structure could be distinguished. It is 

 not unusual to find all of the nuclei within the egg in repose at the 

 same time, as mitosis is very rapid, and the subsequent resting period 

 relatively long; thus, although nuclei in different regions are often 

 found to be in different phases of division, nearly all of the sections 

 made from eggs in preblastodermic stages show every nucleus in a 

 resting condition. Each nucleus is in repose at this time (Fig. 19), 

 but the cytoplasm accompanying it is still actively engaged in its 

 migration toward the periphery. The cytoplasm surrounding the 

 nuclei reaches the "Keimhautblastem" and the granular pole-disc 

 simultaneously, the latter at this point occupying the inner portion 

 of the former as already described in the preceding chapter. 



Each nucleated mass of cytoplasm that comes within the limits of 

 the pole-disc presses outward a mass of granules equal to the area 

 of its fore-end. The whole disc is thus indented in as many places 

 as there are protoplasmic masses striking it (Fig. 8 and Stage A). 

 Fig. 20 illustrates two stages (a and b) in the early genesis of the 

 pole-cells, and also sliows at the extreme right a third nucleus (c) 



