R, Rostellum (barren stigma).
This column stands up from the base of the flower, almost at right angles to the lip, and it bears at the top an anther, in the two hollow lobes of which are concealed the two pollen-masses, each with its caudicle terminating below in a roundish gland, concealed at first in the pouch-like rostellum at the front of the column.
These complex organs have apparently arisen by the increase in depth and differentiation of an accessory sucker such as is borne on the phyllidia of the former group. Lastly, the scolex of the more familiar Taeniidae (Tetracotylea) carries a rostellum encircled with hooks and four cup-shaped suckers the margins of which do not project beyond the surface of the body.
In one genus (Polypocephalus) the place of a rostellum is taken by a crown of retractile tentacles.
A peculiar modification of this type of scolex occurs in the Echinobothridae, in which the axial part of the organ (the rostellum) is elongated and provided with several rows of hooks, whilst the phyllidia have partially fused.
The thicker portion develops a terminal muscular rostellum and two or four suckers, the thinner end (" tail ") is vesicular, more or less elongated, and contains the six embryonic hooks.
(From Lankester's Treatise on Zoology, part iv.) the base of the tail; nervous and muscular systems arise; and finally the rostellum and suckers become completely enclosed in the sac formed by the lateral extension of the " hind-body."
A rostellum and four phyllidia united to form a pair.
3) without hooklets on the rostellum; intestine of man.
In orchids each of the pollen-masses has a prolongation or stalk (caudicle) which adheres to a prolongation at the base of the anther (rostellum) by means of a viscid gland (retinaculum) which is either naked or covered.