mesonephroi

It was found that embryonic viscera which in normal specimens are devoid of innervation, such as the mesonephroi, or which become scarcely innervated only in late developmental stages, such as the sex glands, the thyroid, the parathyroid and the spleen, were loaded with sympathetic nerve fibers during early embryonic stages. [

Nobel Lecture The Nerve Growth Factor: Thirty-Five Years Later 1986