External Shape Well-developed at www.japanese-home-gardens.com

The external shape well-developed shape of well-developed crystals reflects precisely the symmetry of the unit cell. The unit cell of sodium chloride is a cube; the crystal shape of halite is therefore also a cube, or another closely related form such as an octahedron. The elements of symmetry that can be found in crystals are axes, planes and centres. A symmetry axis is such that an object (including a crystal) rotated around it by a given angle will produce a configuration identical to the original one. The number of such rotations to obtain a full 360° turn is the order of the axis.

Present day snakes are characterized by an absence of external shape well-developed limbs and eyelids (neither of which distinguishes them from all lizards) coupled with lower jaws whose rami are not fused but united anteriorly by a more or less elastic ligament, and by vertebrae so numerous that there may be several hundred. Though limbs are absent several families of snakes exhibit in their skeletons vestiges of a limb girdle of which external shape well-developed evidence is displayed only by boas and pythons in the shape of a claw on either side of the transverse anus, from which a pair of evertible hemipenes can be extruded during mating.

In the simpler forms of living material, respiration can be viewed as a single-stage process. The structure that utilizes oxygen and forms carbon dioxide is in direct contact with the external shape well-developed environment. In more complex organisms, specialized structures have been developed which are at a distance from the sites where cellular metabolism takes place. Mechanisms for gas transport are required between these locations. The processes relating to the interchange of gases between the environment and the body are usually termed external shape well-developed respiration, while those exchanges occurring within the organism itself are called internal respiration.