Ichthyodea, characters of, 577, 579.
Incongruence; in Lepidopterous families, 437;
genera, 446, 449;
species, 451;
varieties, 456;
two kinds of, 458, 502;
in Hymenoptera, 481;
in Diptera, 488;
different forms of, 503;
dependent upon action of environment, 505, 507, 508.
Inheritance; homochronic, 63, 431;
definition of cyclical, 66;
limited by sex, 68.
Insects, ancestry of, 493.
Intermaxillary gland of Axolotl, 623.