lODAMOEBA BUTSCHLII II7 



(figs. 2 J, M), and of variable shape. Usually they are more or less 

 rounded. At times two (fig. 2 K) or even three separate masses of 

 glycogen may be present in a cyst. They gradually disappear from the 

 cysts if they are kept for some days, being apparently absorbed. It 

 thus seems probable that they represent a reserve of food material. 



In addition to the volutin granules and the glycogen mass, the 

 cyst of /. hiitschlii contains a single nucleus. This differs in structure 

 from that of the active amoeba, and to understand the difference it is 

 necessary to study the changes which occur during encystation. I 

 shall therefore revert to the active form at this stage, in order to 

 describe this process. 



Unlike E. histolytica and £. coli, I. hiitschlii does not undergo any 

 diminution in size prior to encystation. The precystic amoebae are, in 

 fact, some of the largest forms of the organism met with ; so that they 

 are not, in this respect, comparable with the " miuntn " forms of E. 

 histolytica. Amoebae which are preparing to encyst get rid of all the 

 food contained in their vacuoles, and their cytoplasm becomes beautifully 

 clear and transparent. At the same time the nucleus increases in size 

 (see figs. 35, 36, PI. II). This increase is chiefly noticeable in the 

 zone between the karyosome and the nuclear membrane. This zone, 

 which contains the layer of granules of " peripheral chromatin " in the 

 active amoeba (figs. 32, 34, PI. II) now becomes filled with much more 

 numerous granules, often forming several distmct layers (figs. 35, 36). 

 At this stage the nucleus has increased from about 2 — 2-5 fj, in the active 

 form to 3 ^ or even 4 /x in diameter. The amoebae are now strikingly 

 different from the vegetative forms. Their protoplasm is clear and 

 white in the living organism, and in well fixed and stained specimens 

 appears finely alveolate and remarkably uniform (figs. 35, 36). These 

 amoebae are very sluggish, soon become non-motile, and then more or 

 less rounded, when they secrete their cyst walls (fig. 37). 



With the formation of the cyst wall further changes take place within 

 the organism. The encysting, or partly encysted, amoeba shows at first 

 a small and diffusely stained brown patch in its protoplasm when 

 examined in iodine solution. This is the forerunner of the glycogen 

 mass, and it can be seen to become larger, more deeply stainable, and 

 with a definite contour, in individuals at later stages in development. 

 Simultaneously the volutin granules appear in the cytoplasm. At first 

 they are extremely small, and indistinct, but later they are seen to be 

 larger and highly refractile. At the time of their formation they do not 

 seem to have any definite relation to the nucleus or the glycogen mass, 

 but make their appearance in any part of the cytoplasm. The most 

 striking change occurs, however, in the nucleus. The karyosome, which 

 is central in the active and precystic amoebae (figs. 32-36), gradually 

 passes towards the periphery (fig. 37), until it lies as a large and compact 

 mass in contact with the nuclear membrane in the fully-formed cyst 

 (figs. 40-42). Fig. 37 shows an organism which has just formed its cyst 

 wall. The volutin granules are already fairly numerous : the glycogen 

 mass was small, and is represented by a small vacuole in the stained 

 specimen. The karyosome is passing to the periphery of the nucleus, 

 and the abundant "peripheral chromatin" has a characteristic appear- 

 ance. Comparison of this figure with fig. 36 — an earlier stage — and 

 fig. 40 — a mature cyst — will show at a glance the chief changes which 

 occur during encystation. 



