ria. These
conclusions have been vigorously attacked, more especially by
Dejerine of Paris (_La Presse medicale_, July 1906 and elsewhere).

APHELION (from Gr. [Greek: apo], from, and [Greek: helios], sun), in
astronomy, that point of the orbit of a planet at which it is most
distant from the sun. Apogee, Apocentre, Aposaturnium, &c. are terms
applied to those points of the orbit of a body moving around a centre of
force--as the Earth, Saturn, &c.--at which it is farthest from the
central body.

APHEMIA (from Gr. [Greek: a], without, and [Greek: pheme], speech), in
pathology, the loss of the power of speech (see APHASIA).

APHIDES (pl. of Aphis), minute insects, also known as "plant-lice,"
"blight," and "green-fly," belonging to the homopterous division of the
order Hemiptera, with long antennae and legs, two-jointed, two-clawed
tarsi, and usually a pair of abdominal tubes through which a waxy
secretion is exuded. These tubes were formerly supposed to secrete the
sweet substance known as "honey-dew" so much sought after by ants; but
this is now known to come from the alimentary canal. Both winged and
wingless forms of both sexes occur, and the wings when present are
normal in number, that is to say two pairs. Apart from their importance
from the economic standpoint, Aphides are chiefly remarkable for the
phenomena connected with the propagation of the species. The following
brief summary of what takes place in the plant-louse of the rose (_Aphis
rosae_), may be regarded as typical of the family, though exceptions
occur in other species: Eggs produced in the autumn by fertilized
females remain on the plant through the winter and hatching in the
spring give rise to female individuals which may be winged or wingless.
From these females are born parthenogenetically, that is to say without
the intervention of males, and by a process that has been compared to
internal budding, large numbers of young resembling their parents in
every particular except size, which themselves reproduce their kind in
the same way. This process continues throughout the summer, generation
after generation being produced until the number of descendants from a
single individual of the spring-hatched brood may amount to very many
thousands. In the autumn winged males appear, union between the sexes
takes place and the females lay the fertilized eggs which are destined
to carry the species through the cold months of winter.