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A class of air-breathing oviparous vertebrates, usually covered with scales or bony plates. The heart generally has two auricles and one ventricle. The development of the young is the same as that of birds.

That part of the eye of an invertebrate which corresponds in function with the retina of a vertebrate.

ur united cells which occupy the axial part of the ocelli, or ommatidia, of the eyes of invertebrates, and contain the terminal nerve fibrillæ. See Illust. under Ommatidium.

One of the group of pigmented cells which surround the retinophoræ of invertebrates. See Illust. under Ommatidium.

A comprehensive group of vertebrates, comprising the reptiles and birds.

An extinct order of birds having a long vertebrated tail with quills along each side of it. Archæopteryx is the type. See Archæopteryx, and Odontornithes.

One of the small scalelike structures covering parts of some invertebrates, as those on the wings of Lepidoptera and on the body of Thysanura; the elytra of certain annelids. See Lepidoptera.

the pronephric duct. -- Segmental organs. (a) (Anat.) The embryonic excretory organs of vertebrates, consisting primarily of the segmental tubes and segmental ducts. (b) (Zoöl.) The tubular excretory organs, a pair of which often occur in each of several segments in annelids. They serve as renal organs, and often, al…

hard calcareous or chitinous external covering of mollusks, crustaceans, and some other invertebrates. In some mollusks, as the cuttlefishes, it is internal, or concealed by the mantle. Also, the hard covering of some vertebrates, as the armadillo, the tortoise, and the like.

The bony and cartilaginous framework which supports the soft parts of a vertebrate animal.

The skeleton of the head of a vertebrate animal, including the brain case, or cranium, and the bones and cartilages of the face and mouth. See Illusts. of Carnivora, of Facial angles under Facial, and of Skeleton, in Appendix.

The outer, or parietal, one of the two lamellæ into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the body and the amnion are developed. See Splanchopleure.

One of the actual or ideal serial segments of which an animal, esp. an articulate or vertebrate, is composed; somatome; metamere. -- So*mit`ic, a.

A small sac connected with the female reproductive organs of insects and many other invertebrates, serving to receive and retain the spermatozoa.

irregularly shaped bone in front of the occipital in the base of the skull of the higher vertebrates. It is composed of several fetal bones which become united the adult. See Alisphenoid, Basisphenoid, Orbitosphenoid, Presphenoid.

Any small calcareous or siliceous body found in the tissues of various invertebrate animals, especially in sponges and in most Alcyonaria.

ine or spines. Spinal accessory nerves, the eleventh pair of cranial nerves in the higher vertebrates. They originate from the spinal cord and pass forward into the skull, from which they emerge in company with the pneumogastrics. -- Spinal column, the backbone, or connected series or vertebræ which forms the axis of…

The inner, or visceral, one of the two lamellæ into which the vertebrate blastoderm divides on either side of the notochord, and from which the walls of the enteric canal and the umbilical vesicle are developed. See Somatopleure. -- Splanch`no*pleu"ric, a.

A peculiar glandlike but ductless organ found near the stomach or intestine of most vertebrates and connected with the vascular system; the milt. Its exact function in not known.

a thin splintlike bone on the inner side of the proximal portion of the mandible of many vertebrates.