This looks like a "Tintenkuli", the German term that translates as 'ink worker'. They were produced in Hamburg starting in the early 1920's.
Its hard to tell from the pictures what the material is, but early Tintenkulli pens were made from ebonite or cellluloid and were lever fillers. I notice that there is a lever on the side of the barrel. Given the age, the sac may need to be replaced, or at lease reglued. Sacs were made of rubber, and the usual adhesive was shellac.
Tintenkuli were 'stylographic pens'. Stylographic pens were invented in the US around the beginning of the 20th century, and were initially intended to be an alternative to traditional fountain pens. They never gained a lot of popularity, but around 1920, Dr. Wilhelm Riepe became interested in the design, and took it back to Germany where he created the "Tintenkuli", a lever-filled stylographic pen made from either hard rubber (ebonite) or celluloid. His "Tintenkuli" never displaced conventional fountain pens, but did morph into what later became know as ruling or technical pens. Technical pens differ from ordinary fountain pens in that they were designed to be used with pigment-based ink that would clog the feed of ordinary fountain pens. To prevent clogging, the nib is a hollow tube, with a weighted pin that moves in and out to keep ink flowing through the nib. That pin is fractionally longer than the nib, so when the nib touches paper the pin is lifted slightly to regulate ink flow. There are three major manufacturers of these pens - all in Europe - Staedler, Rotring, and Koh-i-Noor (and today, Koh-i-Noor has a factory in the US). Technical pens came in various nib sizes, denoted numerically by the line width in mm. Standard pens come with stainless steel nibs, but carbide nibs were available for use in instances where the pens were to be used on highly abrasive linen drafting material.
Modern technical pens have a removable reservoir that is either filled using an eyedropper or from an ink bottle with an eye-dropper-like cap. and modern Koh-i-Noor pens have a white body and screw cap. Older Koh-i-Noor pens were black plastic with a colorcoded finial to differentiate nib sizes, and were piston fillers. It was possible to use ordinary fountain pen ink in them. I used one when I was in college to take notes - one of the quirks of technical pens is that the barrel has to be held almost vertical with the nib perpendicular to the paper, so they are better suited for lettering rather than cursive writing, and I found that forced me to write more slowly which means that the notes that I took were actually legible.
