Decdpoda.
1. A large and important order of Crustacea (arthropoda) including shrimps, prawns, lobsters, crayfishes and crabs. 2. An order of Cephalopoda (Mollusca) including cattle fish and squids.

Decidua. Mucous membrane (endometrium) lining uterus in the thickened and modified form; it acquires during pregnancy in many mammals (not in ungulates, see placenta). Some or all of the deciduas come away with the placenta at birth.

Deciduous teeth. Milk teeth. First of the two sets of teeth which most mammals, have; similar to the second (permanent) set which replaces it except in having grinding teeth corresponding only to the premolars, not to the molars, of the set.

Deficiency disease. Disease due to deficiency of some essential food substance, e.g. vitamin mineral element, or essential amino acid.

Dehiscent.
Opening to liberate the seeds, e.g. pea, viola, poppyl

Dehydration. The process by which water is removed from any substance. It is utilized unfreeze-drying for the preservation of material and in the removal of water from microscopical preparation where it is necessary to use substances which are immixible with water.

Dehydrogenase. Enzyme which catalyses oxidation of substrate by removing hydrogen from it. Most oxidizing enzymes are the dehydro-genases.

Deletion mapping. The use of overlapping deletions to locate the position of a gene on a chromosome map.

Delimitation.
The formal statement in taxonomy that defines and limits the characters.