Glands.

 A gland is a secretory organ which may exist as a separate organ such as the liver, pancreas, and spleen; or may be simple a layer of cells as the simple tubular glands of the alimentary canal, body cavities, etc. all glands have a reach blood supply. Their special function is to select from the blood stream certain substances which they then elaborate into their important juices or secretions.

  There is a tremendous variety of glands each with its different function making a collective description and classification difficult. A simple classification is as follow:

  Glands which pour their secretion directly on to the surface include the sweet glands, sebaceous glands, and the gastric and intestinal glands.

 Glands which pour their secretion indirectly by means of ducts on to the surface include the salivary glands, pancreas, and liver.

Ductless glands. These from the group described as endocrine organs. These are glands of internal secretion. A great deal of the well being of the body depends on these glands which through their secretions exert an important chemical control on the function of the body.