Howdy,
If you ungroup the image a number of times, you may see its parts. It is also often helpful to view the image in Inkscape in Outline mode.

- immature.jpg (84.49 KiB) Viewed 1608 times
As you can see from the screenshot, the features are closed paths. (The status bar will report fill, no stroke on selected objects)
So, the paths may need to be traced to create stroked paths.