Ichthyomorpha

(Gr. ichthus; morphe, shape). An order of Amphibians, often called Urodela, comprising the fish-like Newts, etc.

Ichthyophthira

(Gr. ichthus; phtheir, a louse). An order of Crustacea comprising animals which are parasitic upon Fishes.

Ichthyopsida

(Gr. ichthus; opsis, appearance). The primary division of Vertebrata, comprising the Fishes and Amphibia. Often spoken of as the Branchiate Vertebrata.

Ichthyopterygia

(Gr. ichthus; pterux, wing). An extinct order of Reptiles.

Ichthyosauria

(Gr. ichthus; saura, lizard). Synonymous with Ichthyopterygia.

Ilium

The haunch-bone, one of the bones of the pelvic arch in the higher Vertebrates.

Imago

(Lat. an image or apparition). The perfect insect, after it has undergone its metamorphoses.

Imbricated

Applied to scales or plates which overlap one another like tiles.

Incisor

(Lat. incido, I cut). The cutting teeth fixed in the intermaxillary bones of the Mammalia, and the corresponding teeth in the lower jaw.

Inequilateral

Having the two sides unequal, as in the case of the shells of the ordinary bivalves (Lamellibranchiata). When applied to the shells of the Foraminifera, it implies that the convolutions of the shell do not lie in the same plane, but are obliquely wound round an axis.

Inequivalve

Composed of two unequal pieces or valves.

Infundibulum

(Lat. for funnel). The tube formed by the coalescence or apposition of the epipodia in the Cephalopoda - commonly termed the " funnel" or "siphon."

Infusoria

(Lat. infusum, an infusion). A class of Protozoa, so called because they are often developed in organic infusions.

Inguinal

(Lat. inguen, groin). Connected with, or situated upon, the groin.

Inoperculata

(Lat. in, without; operculum, a lid). The division of pul-monate Gasteropoda in which there is no shelly or horny plate (operculum) by which the shell is closed when the animal is withdrawn within it.

Insecta

(Lat. inseco, I cut into). The class of Articulate animals commonly known as Insects.

Insectivora

(Lat. insectum, an insect; voro, I devour). An order of Mammals.

Insectivorous

Living upon Insects.

Insessores

(Lat. insedeo, I sit upon). The order of the Perching Birds, often called Passeres.

Interambulacra

The rows of plates in an Echinoderm which are not perforated for the emission of the "tube-feet."

Intermaxillae or Praemaxillae

The two bones which are situated between the two superior maxillae in Vertebrata. In man, and some monkeys, the praemaxillae anchylose with the maxillae, so as to be irrecognisable in the adult.

Intussusception

(Lat. intiis, within ; suscipio, I take up). The act of taking foreign matter into a living being.