1. In Rhabdomonas costata Pringsheim the osmiophil material, as shown in Weigl preparations, is very variable in amount and arrangement.

2. In the majority of organisms it takes the form of a large osmiophil body lying beneath the reservoir, to which it appears to be connected by a short osmiophilic canal-like structure. Small scattered osmiophil granules are aggregated in the region of the reservoir and sparsely distributed throughout the cytoplasm.

3. In some individuals the osmiophil ‘canal’ is absent.

4. The osmiophil body may also be present as a ring with a thickened osmiophil cortex and an osmiophobe centre.

5. The behaviour of the osmiophil substance during division is as follows: the body loses its canal and spreads along the lower wall of the reservoir; as division proceeds it becomes divided into two masses, and when the organism separates into daughter individuals each monad contains nearly equal quantities of the osmiophil substance. There is thus a definite dictyokinesisin Rhabdomonas.

6. In a few instances the osmiophil material is carried over whole to one of the two organisms formed by division.

7. In some normal (non-dividing) individuals two osmiophil bodies and their respective canals are found.

8. From the fact that the osmiophil material in Rhabdomonas is demonstrable after the metazoan Golgi Weigl technique, is resistant to bleaching, and is separated out evenly in most cases during division, it is believed to represent the Golgi apparatus in this organism.

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