i. 52;

on the contest in man between right and wrong, i. 104; on the physical weakness of man, i. 156; on the primitive civilisation of man, i. 181; on the plumage of the male Argus pheasant, ii. 91; on _Urosticte Benjamini_, ii. 151; on the nests of birds, ii. 167; on variety as an object in nature, ii. 230.

_Argynnis aglaia_, colouring of the lower surface of, i. 396.

_Aricoris epitus_, sexual differences in the wings of, i. 345.

ARISTOCRACY, increased beauty of the, ii. 356.

ARMS, proportions of, in soldiers and sailors, i. 116; direction of the hair on the, i. 192.

ARMS and hands, free use of, indirectly correlated with diminution of canines, i. 144.

ARREST of development, i. 121, 122.

ARROW-HEADS, stone, general resemblance of, i. 233.

ARROWS, use of, i. 232.

ARTERIES, variations in the course of the, i. 108.

ARTERY, effect of tying, upon the lateral channels, i. 116.

ARTHROPODA, i. 328.

ARTS practised by savages, i. 234.

ASCENSION, coloured incrustation on the rocks of, i. 326.

ASCIDIA, affinity of the lancelet to, i. 205; tadpole-like larvae of, i. 205.

ASCIDIANS, i. 324; bright colours of some, i. 322.

_Asinus_, Asiatic and African species of, ii. 306.

_Asinus taeniopus_, ii. 306.

ASS, colour-variations of the, ii. 305.

_Ateles_, effects of brandy on an, i. 12; absence of the thumb in, i. 140.

_Ateles beelzebuth_, ears of, i. 23.

_Ateles marginatus_, colour of the ruff of, ii. 291; hair on the head of, ii. 109; on the recognition of a dog by a turkey, ii. 110; on the selection of a mate by female birds, ii. 307.

_Ateuchus_, stridulation of, i. 384.

_Ateuchus cicatricosus_, habits of, i. 376.

_Athalia_, proportions of the sexes in, i. 314.

ATTENTION, manifestations of, in animals, i. 44.

AUDOUIN, V., on a hymenopterous parasite with a sedentary male, i. 273.

AUDUBON, J. J., on the pugnacity of male birds, ii. 43, 48; on _Tetrao cupido_, ii. 50; on _Ardea nycticorax_, ii. 51; on _Sturnella ludoviciana_, ii. 51; on the vocal organs of _Tetrao cupido_, ii. 56; on the drumming of the male _Tetrao umbellus_, ii. 61; on sounds produced by the nightjar, ii. 63; on _Ardea herodias_ and _Cathartes jota_, ii. 68; on the spring change of colour in some finches, ii. 86; on _Mimus polyglottus_, ii. 116; on the turkey, ii. 119, 121; on variation in the male scarlet tanager, ii. 126; on the habits of _Pyranga aestiva_, ii. 167; on local differences in the nests of the same species of birds,