Amphioxus: The most simply organized animal having a dorsal notochord. It is classified among the Acrania in contradistinction to the craniate Chordates which make up the bulk of the vertebrates.
Angiosperms: The higher plants, which have their seeds enclosed in seed-vessels.
Anthropoid Apes: Apes of the family Simiidæ, which approach man most closely in their organization, namely, the chimpanzee, the gorilla, the gibbon, and orang-utan.
Antibody: Chemical substances produced in the blood in reaction to the injection of antigens or toxic substances and capable of counteracting or neutralizing said substance. Such antibodies are specific for determinate antigens.
Antigen: Any substance that causes the production of special antibodies in the blood of susceptible animals, after one or several injections.
Arthropods: The phylum of exoskeletal invertebrates comprising crustaceans, arachnida, insects, etc.
Atavism: The resemblance to an ancestor more distant than the parents.
Automatism: A spontaneous action, not in response to recognizable stimuli.
Basichromatin: That portion of a cell’s nuclear network which contains nuclein and is deeply stained by basic dyes.
Biparental: Derived from two progenitors, i.e., a father and mother.