42 THE AMOEBAE LIVING IN MAN 



I cannot count the " chromosomes," however, and I cannot resolve the 

 structures here seen into a typical mitotic figure. Similar stages have 

 similar appearances, but the numbers of "chromosomes" and fibres 

 appear to be variable. In later stages (fig. 46) the figures are even worse 

 to study, and show a most confusing arrangement — or apparent lack 

 of arrangement — of stainable threads, masses, and granules. There are, 

 however, usually several definite achromatic fibres which pass from one 

 end of the spindle to the other. They can sometimes be seen with great 

 clearness, and even counted (fig. 47), but their number seems to be 

 inconstant and their arrangement often varies. Not infrequently — as in 

 fig. 47 — they are crossed or twisted towards the middle of the spindle. 

 {This figure is drawn from an iron-haematoxylin specimen, very strongly 

 differentiated.) 



The greatly elongated spindle now constricts in the middle, its 

 internal structure undergoing no obvious change (fig. 48). The con- 

 striction becomes more marked (fig. 49), and the two ends now pull 

 apart (fig. 50), but still remain connected for some time by a thread. 

 This then snaps, and the resulting daughter nuclei become rounded and 

 vesicular (fig. 51). At this stage they begin to show a definite arrange- 

 ment of the chromatin once more — some of the granules passing to the 

 periphery, and one of them, slightly larger or more conspicuous than 

 the others, often being recognizable as the karyosome of the new nucleus. 

 During the earlier stages of division the spindle is typically sharply 

 pointed ; and the points frequently persist until quite a late stage (fig. 50). 

 Sometimes the ends become rounded earlier, however, before the 

 daughter nuclei are fully formed (fig. 49). The specimens figured have 

 been selected to show these slight variations. 



The end stages in fission are very simple. The two daughter nuclei 

 undergo reconstruction, into the form of the resting nucleus, by gradual 

 rearrangement of the chromatin granules on the nuclear membrane and 

 differentiation of the karyosome in the centre. The whole organism 

 becomes elongated, and the nuclei pass to its ends (fig. 52). A constric- 

 tion then appears in the middle of the animal (fig. 53) and gradually 

 deepens until complete constriction into two is effected (fig. 54). Rem- 

 nants of the thread which originally connected the two daughter nuclei 

 often persist for a considerable time, as little knobs or outgrowths on the 

 daughter nuclei (cf. figs. 52, 53). Late stages in fission, it may be added, 

 are extremely difficult to obtain. This is because the dividing amoebae 

 are usually tightly packed together in the bases of the ulcers : and when 

 division of the cytoplasm takes place, they still remain closely crowded. 

 It is thus very difficult, in sections, to be certain whether two small 

 amoebae in close apposition are dividing or divided forms, or merely 

 two small unrelated organisms accidentally in contact. Figs. 53 and 54 

 were drawn from specimens lying in the mucus on the surface of an 

 ulcer, where they were somewhat isolated. They were found with 

 difficulty, as dividing organisms are rare in such situations. 



The foregoing account of the nuclear division is based, as already 

 noted, on a study of a large number of dividing organisms. It is some- 

 what unsatisfactory because the nuclear divisions are so peculiar that they 

 are difficult to describe in ordinary terms. Whether chromosomes are 

 present I am still unable to decide, as the nuclear figures are very difficult 

 to interpret. The illustrations are drawn as carefully as possible, so that 

 the reader will, I hope, be able to put his own construction on the actual 



