1. Optimum growth of E. invadens occurred in HSre + S in the presence of Bact. coli, at 24–30° C. The amoebae could not be ‘trained’ to grow above 35° C.

2. The amoebae ingested normal rat erythrocytes, but not those of chick or frog.

3. Mass encystation occurred only under conditions which favoured the growth of the amoebae, but was not dependent on an acceleration in growth rate; in certain strains, an increased production of cysts was correlated with the depletion of starch in the medium.

4. The amoebae were always killed by treatment with N/20-HCl for 1 hr. at room temperature, although usually they did not survive after treatment for only 10 min. At room temperature, the cysts survived treatment with N/10-HC1 for at least 6 days, and with 0·002% HgCl2 for at least 4 hr.

5. The amoebae of E. invadens were adversely affected by aerobic conditions.

6. The amoebae could survive for up to 35 days at 8° C. but for not more than 7 days at 37° C. The cysts survived for at least 14 days at 8° C., for 7, but not 11, days at 24° C., and for less than 7 days at 37° C.

7. It is suggested that, in view of the morphological identity of E. aulastomi, E. invadens, E. moshkovskii and E. histolytica, and the fact that the amoebae of these groups form a series growing at increasingly higher temperatures, these four organisms constitute subspecies rather than full species. The taxonomic status of E. ranarum is still open to question.

By means of ultra-thin sections for electron microscopy it has been possible to observe intra-nuclear changes in the polyhedrosis of larvae of Tipula paludosa. The virus rods arise in the centres of the greatly enlarged nuclei of blood cells. Thin-walled vesicles, apparently filled with fluid, form round individual virus rods and collect in masses on the inner wall of the nuclear membrane. Crystallization then begins, starting at the edge against the nuclear membrane. The vesicles are gradually compressed round the rods, eventually forming a capsule. Sections through free virus particles show them to be enclosed in a membrane, a second inner membrane round the substance of the rod may also be present.

There appears to be no capsule round the free virus particles such as encloses the virus particles inside the polyhedral crystal.