Vulcan reproductive gland

From Memory Alpha, the free Star Trek reference

The Vulcan reproductive gland is a part of the Vulcan body that has, as the name implies, an important function in Vulcan reproduction.

In 2375 the Doctor hosted a slideshow of some of his pictures on the holodeck. Among those pictures was a huge image of the Vulcan reproductive gland. The Doctor marvelled at its composition and the subtle variations in color. (VOY: "Nothing Human")