Standard Dropper Filled (or eyedropper filled) fountain pens
This is the original “fountain pen.” Rather than dipping the nib to write, the ink “fountain” is within the pen itself.
To fill the pen barrel with ink, unscrew the section and remove it. Fill the barrel with ink using a dropper, and then replace the section. Simple idea. The pen holder (barrel) is the reservoir for ink. The challenge that had to be overcome for this to work was how to find a way for ink to flow slowly, but not leak, and for air to return to the barrel to take the place of the ink that has run out. During the 1880s and 1890s, there were many styles of feeds (the black rubber part under the nib) each trying to find an ideal way to feed ink to the nib while not blobbing or causing skipping while in use.