BIXIC'LKATK CKl.LS L\ TlSSUli CI I/riKKS. 91 



showed almost constant minor variations in contour; it seemed to be composed of 

 a row of small refractive bodies (chromosomes) undergoino; constant, slow, and very 

 slight movements. From this characteristic formation, situated as it was in a 

 diamond-shaped field, surrounded, as before, by a granular ring of refractive globules 

 and mitochondria, the metaphase of mitosis was easily recognized. This stage was 

 drawn at 6'> 50'" j). m. (67) and would appear like figure 15 if fixed and stained. 

 The cell is somewhat smaller and more condensed than that seen in 66, and the 

 appearance plainly indicates that the centrosome has divided and that each part 

 is performing its usual function at a pole of the spindle. The actual division of the 

 centrosome was not ob.served. 



After a short time the ])late was seen to split, and the two halves, retaining 

 their parallel relationship to one another, moved to opposite poles of the cell, and 

 there remained, thus marking the anaphase. Figure 16, from a fixed preparation 

 of a mononucleate cell, represents this stage. Almost immediately thereafter the 

 granules and fat globules midway from the poles of the cell were .seen to move inward 

 as though a constriction were occurrmg about the nuclear area at this zone; the 

 result was a dumb-bell-shaped mass within the elongated cell, formed of the nuclear 

 area and surrounding protoplasm. Almost at once the cell membrane itself was 

 seen to be undergoing constriction at this point, as shown in 68, at 7'" 05"' p. m. At 

 the same time the nuclear areas at either end of the cell commenced to become free 

 from granules of fat and other refractive material and the cell outline became larger, 

 showing that the cell was flattening out and that the daughter nuclei were becoming 

 reconstituted in the telophase. 



That the intracellular i)ressure is considerably increased during this process is 

 shown by the bulging outward of certain portions of the cell membrane, as illustrated 

 in 68, to form bubble-like protuberances. Frequently the granules and fat globules 

 may be seen to rush out into these evaginations, indicating the formation of cell 

 currents, where j^ressure has been suddenly released, through giving way and 

 stretching of localized areas of the cell wall. These i)rotuberances soon flatten out, 

 lie close to the cover-slip and expand, becoming armed with hyaline borders pos- 

 sessed of amoeboid movement (Harrison, 1913, p. 67). The end of the cell opposite 

 the connection with the daughter cell thus appears fimbriated, as shown by Lewis 

 and Lewis (12c, fig^. 8 and 10). These refractive borders act as pseudopodia to 

 anchor the cell to the cover-slip and to drag the daughter cells apart. 



The reforming nuclei, now more widely separated, and showing wider and clearer 

 areas in the cell protoplasm, are seen in 69 at 7'' 25'" p. m., and at this time the cell 

 was very much constricted, with the nuclei more widi^ly s(>i)arated. The constricted 

 zone is somewhat more highly refractive than the surrounding tissue and resembles 

 a short thread. Here also the cell proce.s.ses are seen to be feeling their way outward 

 and to be pulling the two daughter cells apart. The stage corresponding to this 

 in the fixed preparations is shown in figure 17; here the chromatin is a closely 

 clumped, darkly staining mass, and the individual chromosomes are becoming 

 resolved into smaller granules. These subsequently become scattered, and apj^ear 

 in the later definitive, more lightly staining, nucleus as in figure 18. A marked 

 expansion of cytojilasm is here to be noted. 



