1. In Copromonas subtilis , Dobell, and Euglena sp. there is a Golgi apparatus consisting of osmiophil material in the form of granules, which are associated with the osmoregulatory mechanism of the cell.
2. Inside the granules, water collects, so that they become spherical vacuoles, identical with what have in the past been called contractile vacuoles (Copromonas) or accessory contractile vacuoles (Euglena viridis).
3. In Euglena viridis, the Golgi apparatus is closely applied to the so-called contractile vacuole, and consists of numerous loaf-shaped osmiophil bodies which undergo a regular series of changes from systole to diastole, and vice versa.
4. In Copromonas, the osmiophil material may form a thick cortex surrounding what has been called the reservoir, it may be attached to the reservoir in fairly regular loafshaped bodies as in Euglena, or it may be completely detached from the reservoir.
5. The so-called contractile vacuoles of Copromonas are vesicles containing water, which are formed on the site of the osmiophil granules.
6. As far as we are able to say at present, the reservoir of Copromonas is indistinguishable from an enlarged contractile vacuole, and new reservoirs probably arise from swollen contractile vacuoles. It is difficult to believe that the reservoir divides into two, as has been claimed by Dobell.
7. During division of Copromonas, two reservoirs can nearly always be found in the early stages before the nucleus becomes dumb-bell shaped. These seem to have originated from the osmiophil vacuoles.
8. The remaining osmiophil material, when present, moves slightly down the cell, occupying a place in the mid-line. When the new cell-wall between the two organisms has passed down, about one-third the length of the dividing monad, the osmiophil material splits into two sub-equal groups and is so divided between the two organisms. There is therefore a definite dictyokinesis to be found in Copromonas.
9. Just at or after this period, the osmiophil material may become scattered about the upper middle and upper region of the dividing monads, but finally becomes situated in the region of the reservoir.
10. The osmiophil material (Golgi apparatus) persists throughout conjugation and encystment, even when a reservoir cannot be found.
11. There is a rhizoplast joining the basal granule of the flagellum with the intra-nuclear nucleolo-centrosome, and an axostyle is present, passing from the basal granule to the posterior end of the organism.
12. During cell division, the basal granule divides into two and appears to lose its connexion with the two nucleolo-centrosomes of the dividing nucleus. The axostyle appears to be absorbed in the early stages of division and cannot be stained at this epoch, but reappears in each moiety of the dividing organism, when the nucleus is dumb-bell shaped. It appears to reform when the two basal granules have taken their definitive position at the anterior end of the cells.
13. We agree with Wenyon that one flagellum passes over intact to one of the daughter cells at division, the other flagellum arises from the other basal granule.
14. Numerous fat granules are found throughout the organism; what have been called volutin granules in other Protozoa are present in Copromonas, and stain in neutral red.
15. Mitochondria are present mainly in the posterior region of the organism.
The Physiology of Contractile Vacuoles