Ast"cus, optic stalk, [91]

Ast"cus, etina, [98]

Asterolepis, [326], [342]

Atrium, [410]

Auchenaspis (Thyestes), [30], [31], [75], [275], [326], [327], [328], [338]

Auditory apparatus, [355]

Auerbach, plexus of, [447]

Aurelia, [475]

Autonomic nerves, [3]

Balanoglossus, [12], [12], [433], [438], [494]