Definition: Gravel is an environmental material which is composed of pieces of rock that are at least two millimeters (2mm) in its largest dimension and no more than 75 millimeters.
Definition: A structural quality inhering in a bearer by virtue of the bearer's being thicker or more closely packed together; pressed tightly together.
Definition: An eye that consists of a cluster of three or four pit eyes that form a single structural unit but are separated from one another by pigment layers
Definition: A compound eye with no separation between the crystalline-cone layer and the retinula, each rhabdom receiving light only from its own corneal lens.