In addition to shell powder and tissue transfer for superposition, there is a third alternative (probably unsanctioned by traditionalists). The instructions for this piece call for shining a light under the fabric that allows the underlying stitch lines to show through. That was how the right tail veins were stitched. Here's the jury-rigged set-up. The photo was tilted to show the lamp being clamped to shine underneath the fabric.
It takes some getting used to; as the light bulb interferes with my knees and the needle when the needle is underneath. But it is much easier than either shell powder or tissue transfer. And of course this technique only works on thin fabrics, i.e., not on my Antique Mirror piece. (sigh!)