Ovarioles of Notonecta glauca glauca have been treated with vinblastine sulphate (VBL), primarily to examine the effects of the drug on the microtubules which pack the trophic core and nutritive tubes. 10-4 M VBL had little effect on the microtubules. VBL at 10-3 M reduced the number of microtubules in nutritive tubes, while after 2 x 10-3 M VBL microtubules were rare. All 3 concentrations of VBL induced the formation of crystalline structures in the trophic core and nutritive tubes, and to a lesser extent in the nutritive cells and follicle cells. In transverse sections crystals appeared to be composed of distinct hexagonal units and in longitudinal sections crystals showed as dark parallel lines with darker dots at regular intervals along their length. With 10-4 M VBL, the crystals were compact and close to the walls of nutritive tubes, but after treatment with stronger concentrations of VBL the crystals were web-like and scattered over cross-sections of tubes.

In addition to VBL having a destructive effect on the microtubules in the trophic core and nutritive tubes, there was also a reduction in the number of ribosomes. This overall reduction in ribosome quantity could not be attributed to the inhibition of RNA synthesis by VBL.

In regions of ovarioles where microtubules were arranged in parallel masses, as in the nutritive tubes and trophic core, the long axes of crystals were always similarly aligned. Otherwise crystals were randomly oriented. The possible mode of formation, and composition, of crystals is discussed.

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