ed, or "entire."

HOLOTHUROIDEA (Gr. _holothourion_, and _eidos_, form). An order
of _Echinodermata_ comprising the Trepangs.

HOMOCERCAL (Gr. _homos_, same; _kerkol_, tail). Applied to the
tail of Fishes when it is symmetrical, or composed of two equal
lobes.

HYBODUNTS (Gr. _hubos_, curved; _odous_, tooth). A group of Fishes
of which _Hybodus_ is the type-genus.

HYDROIDA (Gr. _hudra_; and _eidos_, form). The sub-class of the
_Hydrozoa_, which comprises the animals most nearly allied to
the Hydra.

HYDROZOA (Gr. _hudra_; and _zooen_, animal). The class of the
_Coelenterata_ which comprises animals constructed after the type
of the Hydra.

HYMENOPTERA (Gr. _humen_, a membrane; _pteron_, a wing). An order
of Insects (comprising Bees, Ants, &c.) characterised by the
possession of four membranous wings.

ICHTHYODORULITE (Gr. _ichthus_, fish; _dorus_, spear; _lithos_,
stone). The fossil fin-spine of Fishes.

ICHTHYOPTERYGIA (Gr. _ichthus_; _pterux_, wing). An extinct order
of Reptiles.

ICHTHYORNIS (Gr. _ichthus_, fish; _ornis_, bird). An extinct genus
of Birds.

ICHTHYOSAURIA (Gr. _ichthus_; _saura_, lizard). Synonymous with
_Ichthyopterygia_.

IGUANODON (_Iguana_, a living lizard; Gr. _odous_, tooth). A genus
of Deinosaurian Reptiles.

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.

INOCERAMUS (Gr. _is_, a fibre; _keramos_, an earthen vessel).
An extinct genus of Bivalve Molluscs.

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 _Echinoid_ which are
not perforated for the emission of the "tube-feet."

INTERMMAXILLAE or PRAEMAXILLAE. The two bones which are situated
between the two superior maxillae in _Vertebrata_. In man, and
some monkeys, the p