In the Metanemertines it is generally situated towards the middle of a lateral transverse groove on either side of the head, as was noticed for Carinella, and as is also present in Polia.
Externally they are easily distinguished by the absence of a longitudinal groove on the skin.
b, c) with a deep groove on its anterior face; this organ is formed by the second pair of maxillae and corresponds therefore to the labium or " lower lip " of biting insects.
The mouth may be circular or four-cornered, and in the latter case the manubrium at the angles of the mouth may become drawn out into four lappets, the oral arms, each with a groove on its inner side continuous with the corner FIG.
Such are the white chrysanthemum-like patches on the rump of the Japanese deer and of the American prong-buck (Antilocapra), and the line of hairs situated in a groove on the loins of the African spring-buck.