On account of some resemblance in form, the Ophreæ are named after insects. The Fly Ophrys differs in no material respect from the other Orchids. The stem or caudicle of the pollinium, instead of being straight, as in the Orchis mascula, is doubly and almost rectangularly bent. The upper membrane of the disc to which the stalk of the pollinium is fixed, being the summit of the rostellum, is exposed to the air, and becomes dry when the flower opens, consequently the disc, though viscid enough on its under-side to stick to an insect’s head, is incapable of shrinking, and causing that depression of the pollinium, characteristic of all the species of Orchis. The labellum has no spur, but at its base, just below the stigma, there is a deep depression representing the nectary; and as the pollinia, which cannot be shaken out of their cells, or pouches, are certainly, though rarely, extracted, Mr. Darwin conceives that small insects crawl along the labellum to its base, strike against one of the pouches, extract a pollinium, and fly with it sticking on their head to another blossom, and that while bending their heads into the hollow at the base of the labellum, the pollinium, owing to its doubly bent stalk, strikes the sticky stigmatic surface, and leaves pollen grains on it. There can be no doubt that this plant is visited occasionally by insects, as it cannot be fructified without them; but it is scentless, and as no nectar has as yet been found in it, their motive for visiting it is unknown. [Illustration: Fig. 83. Epipactis palustris:—Side views of flower, with lower sepals cut away: A, with lip in natural position; B, with lip depressed as by an insect.] The fructification of the Ophrys apifera, or Bee Ophrys, is independent of insects, for the stalks of the pollinia are extremely long, thin, and flexible; and although their viscid discs still remain in their pouches, as soon as the flower expands, and the anther cells or pouches open, the heavy thick ends of the pollinia fall out of their cells, and hang freely down in the air exactly opposite to the stigmatic surface. A breath of air is sufficient to make them vibrate, strike the stigma with their pollen mass, and leave pollen grains on its sticky surface. [Illustration: Fig. 84. Epipactis palustris:—C, side view of flower, with sepals and petals and half the labellum removed: D, front view of column: _a_, anther; _r_, rostellum; _s_, stigma; _l_, labellum.]