APHE´LION (Gr. _apo_, from, and _h[=e]lios_, the sun), that point of the orbit of the earth or any other planet which is remotest from the sun.
Cabbage-leaf Plant-louse (_Aphis brassicæ_)--1, 2. Male, natural size and magnified. 3, 4, Female, natural size and magnified.]
APHIS, a genus of insects (called plant-lice) of the ord. Hemiptera, the type of the family Aph[)i]d[=e]s. The species are very numerous and destructive. The _A. rosæ_ lives on the rose; the _A. fabæ_ on the bean; the _A. hum[)u]li_ is injurious to the hop, the _A. granaria_ to cereals, and _A. lanig[)e]ra_ or woolly aphis equally so to apple trees. The aphides are furnished with an inflected beak, and feelers longer than the thorax. In the same species some individuals have four erect wings and others are entirely without wings. The feet are of the ambulatory kind, and the abdomen usually ends in two horn-like tubes, from which is ejected the substance called honey-dew, a favourite food of ants. (See _Ant_.) The aphides illustrate parthenogenesis; hermaphrodite forms produced from eggs produce viviparous wingless forms, which again produce others like themselves, and thus multiply during summer, one individual giving rise to millions. Winged sexual forms appear late in autumn, the females of which, being impregnated by the males, produce eggs.
APHO´NIA (Gr. _a_, not, and _ph[=o]n[=e]_, voice), in pathology, the greater or less impairment, or the complete loss of the power of emitting vocal sound. The slighter and less permanent forms often arise from extreme nervousness, fright, and hysteria. Slight forms of structural aphonia are of a catarrhal nature, resulting from more or less congestion and tumefaction of the mucous and submucous tissues of the larynx and adjoining parts. Severer cases are frequently occasioned by serous infiltration into the submucous tissue, with or without inflammation of the mucous membrane of the larynx and of its vicinity. The voice may also be affected in different degrees by inflammatory affections of the fauces and tonsils; by tumours in these situations; by morbid growths pressing on or implicating the larynx or trachea; by aneurisms; and most frequently by chronic laryngitis and its consequences, especially thickening, ulceration, &c.