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The last or posterior segment of the thorax in insects. See Illust. of Coleoptera.

One of the smaller cells, or blastomeres, resulting from the complete segmentation of a telolecithal ovum.

The middle segment of the brain; the mesencephalon. See Brain.

opoda, PteropodaScaphopoda, and Lamellibranchiata, or Conchifera. These animals have an unsegmented bilateral body, with most of the organs and parts paired, but not repeated longitudinally. Most of them develop a mantle, which incloses either a branchial or a pulmonary cavity. They are generally more or less covered a…

ldren, and dating back especially to the work of the French-American physician Edouard O. Seguin (1812- 80).

Any fern of the genus Botrychium, esp. B. Lunaria; -- so named from the crescent-shaped segments of its frond.

of the ovum or egg in the first stages of its development; -- called also mulberry mass, segmentation sphere, and blastosphere. See Segmentation.

The process of cleavage, or segmentation, of the ovum, by which a morula is formed.

Having many segments; cleft into several parts by linear sinuses; as, a multifid leaf or corolla.

Divided into many similar segments; -- said of an insect or myriapod.

A muscular segment; one of the zones into which the muscles of the trunk, especially in fishes, are divided; a myocomma.

he hexapod insects, from which they differ in having the body made up of numerous similar segments, nearly all of which bear true jointed legs. They have one pair of antennæ, three pairs of mouth organs, and numerous trachaæ, similar to those of true insects. The larvæ, when first hatched, often have but three pairs of…

(corresponding to the antennules, antennæ, and mandibles), a median eye, and little or no segmentation of the body.

A segmental tubule; one of the tubules of the primitive urinogenital organs; a segmental organ. See Illust. under Loeven's larva.

.), the cartilaginous or bony arch on the dorsal side of the centrum of the vertebra in a segment of the spinal skeleton, usually inclosing a segment of the spinal cord.

A metameric segment of the cerebro-spinal nervous system.

ead, or to the occipital bone. Occipital bone (Anat.), the bone which forms the posterior segment of the skull and surrounds the great foramen by which the spinal cord leaves the cranium. In the higher vertebrates it is usually composed of four bones, which become consolidated in the adult. -- Occipital point (Anat.),…

Cleft or separated into eight segments, as a calyx.

of a pair of scent organs which the larvæ of certain butterflies emit from the first body segment, either above or below.

erally, seeing everything; -- a term applied to eyeglasses or spectacles divided into two segments, the upper being designed for distant vision, the lower for vision of near objects.