In the refraction of light by a convex lens the rays passing through
different parts of the lens are brought to a focus at slightly different
distances, this is called spherical aberration; at the same time
the coloured rays are separated by the prismatic action of the lens and
likewise brought to a focus at different distances, this is chromatic
This term is applied to a peculiar mode of reproduction which
prevails among many of the lower animals, in which the egg produces a
living form quite different from its parent, but from which the
parent-form is reproduced by a process of budding, or by the division of
the substance of the first product of the egg.
A group of fossil, spiral, chambered shells, allied to the existing
pearly Nautilus, but having the partitions between the chambers waved in
complicated patterns at their junction with the outer wall of the shell.
A class of worms in which the surface of the body exhibits a more or
less distinct division into rings or segments, generally provided with
appendages for locomotion and with gills. It includes the ordinary
marine worms, the earthworms, and the leeches.
A great division of the Animal Kingdom characterised generally by
having the surface of the body divided into rings called segments, a
greater or less number of which are furnished with jointed legs (such as
Insects, Crustaceans and Centipedes).
A class of marine Mollusca, or soft-bodied animals, furnished with a
bivalve shell, attached to submarine objects by a stalk which passes
through an aperture in one of the valves, and furnished with fringed
arms, by the action of which food is carried to the mouth.
The highest class of the Mollusca, or Soft-bodied animals,
characterised by having the mouth surrounded by a greater or less number
of fleshy arms or tentacles, which, in most living species, are
furnished with sucking-cups. (Examples, Cuttle-fish, Nautilus.)
An order of Crustaceans including the Barnacles and Acorn-shells.
Their young resemble those of many other Crustaceans in form; but when
mature they are always attached to other objects, either directly or by
means of a stalk, and their bodies are enclosed by a calcareous shell
composed of several pieces, two of which can open to give issue to a
bunch of curled, jointed tentacles, which represent the limbs.
A case usually of silky material, in which insects are frequently
enveloped during the second or resting-stage (pupa) of their existence.
The term `cocoon-stage' is here used as equivalent to `pupa-stage.'
Beetles, an order of Insects, having a biting mouth and the first
pair of wings more or less horny, forming sheaths for the second pair,
and usually meeting in a straight line down the middle of the back.
Plants in which the inflorescence consists of numerous small flowers
(florets) brought together into a dense head, the base of which is
enclosed by a common envelope. (Examples, the Daisy, Dandelion,
A class of plants characterised by having two seed-leaves, by the
formation of new wood between the bark and the old wood (exogenous
growth) and by the reticulation of the veins of the leaves. The parts of
the flowers are generally in multiples of five.
A division of the class Crustacea, having all the segments of the
body usually distinct, gills attached to the feet or organs of the
mouth, and the feet fringed with fine hairs. They are generally of small
A class of animals of very low organisation, and generally of small
size, having a jelly-like body, from the Surface of which delicate
filaments can be given off and retracted for the prehension of external
objects, and having a calcareous or sandy shell, usually divided into
chambers, and perforated with small apertures.
A period of great cold and of enormous extension of ice upon the
surface of the earth. It is believed that glacial periods have occurred
repeatedly during the geological history of the earth, but the term is
generally applied to the close of the Tertiary epoch, when nearly the
whole of Europe was subjected to an arctic climate.
An order or sub-order of Insects, characterised by the possession of
a jointed beak or rostrum, and by having the fore-wings horny in the
basal portion and membranous at the extremity, where they cross each
other. This group includes the various species of Bugs.
That relation between parts which results from their development
from corresponding embryonic parts, either in different animals, as in
the case of the arm of man, the foreleg of a quadruped, and the wing of
a bird; or in the same individual, as in the case of the fore and hind
legs in quadrupeds, and the segments or rings and their appendages of
which the body of a worm, a centipede, &c., is composed. The latter is
called serial homology. The parts which stand in such a relation
to each other are said to be homologous, and one such part or
organ is called the homologue of the other. In different plants
the parts of the flower are homologous, and in general these parts are
regarded as homologous with leaves.
An order or sub-order of Insects having (like the Hemiptera) a
jointed beak, but in which the fore-wings are either wholly membranous
or wholly leathery. The Cicadoe, Frog-hoppers, and Aphides,
are well-known examples.
A class of microscopic Animalcules, so called from their having
originally been observed in infusions of vegetable matters. They consist
of a gelatinous material enclosed in a delicate membrane, the whole or
part of which is furnished with short vibrating hairs (called cilia), by
means of which the animalcules swim through the water or convey the
minute particles of their food to the orifice of the mouth.
A group of greatly altered and very ancient rocks, which is greatly
developed along the course of the St. Laurence, whence the name. It is
in these that the earliest known traces of organic bodies have been
An order of plants represented by the common Peas and Beans, having
an irregular flower in which one petal stands up like a wing, and the
stamens and pistil are enclosed in a sheath formed by two other petals.
The fruit is a pod (or legume).
A group of four-handed animals, distinct from the Monkeys and
approaching the Insectivorous Quadrupeds in some of their characters and
habits. Its members have the nostrils curved or twisted, and a claw
instead of a nail upon the first finger of the hind hands.
The highest class of animals, including the ordinary hairy
quadrupeds, the Whales, and Man, and characterised by the production of
living young which are nourished after birth by milk from the teats (Mammoe,
Mammary glands) of the mother. A striking difference in embryonic
development has led to the division of this class into two great groups;
in one of these, when the embryo has attained a certain stage, a
vascular connection, called the placenta, is formed between the
embryo and the mother; in the other this is wanting, and the young are
produced in a very incomplete state. The former, including the greater
part of the class, are called Placental mammals; the latter, or
Aplacental mammals, include the Marsupials and Monotremes (Ornithorhynchus).
The first or uppermost pair of jaws, which are generally solid,
horny, biting organs. In Birds the term is applied to both jaws with
their horny coverings. In Quadrupeds the mandible is properly the lower
An order of Mammalia in which the young are born in a very
incomplete state of development, and carried by the mother, while
sucking, in a ventral pouch (marsupium), such as the Kangaroos,
Opossums, &c. (see MAMMALIA).
One of the great divisions of the Animal Kingdom, including those
animals which have a soft body, usually furnished with a shell, and in
which the nervous ganglia, or centres, present no definite general
arrangement. They are generally known under the denomination of
`shell-fish;' the cuttle-fish, and the common snails, whelks, oysters,
mussels, and cockles, may serve as examples of them.
Plants in which the seed sends up only a single seed-leaf (or
cotyledon); characterised by the absence of consecutive layers of wood
in the stem (endogenous growth), by the veins of the leaves being
generally straight, and by the parts of the flowers being generally in
multiples of three. (Examples, Grasses, Lilies, Orchids, Palms,
The earliest stage in the development of many Crustacea, especially
belonging to the lower groups. In this stage the animal has a short
body, with indistinct indications of a division into segments, and three
pairs of fringed limbs. This form of the common fresh-water Cyclops
was described as a distinct genus under the name of Nauplius.
The lower part of the pistil or female organ of the flower,
containing the ovules or incipient seeds; by growth after the other
organs of the flower have fallen, it usually becomes converted into the
The male element in flowering plants; usually a fine dust produced
by the anthers, which, by contact with the stigma effects the
fecundation of the seeds. This impregnation is brought about by means of
tubes (pollen-tubes) which issue from the pollen-grains adhering
to the stigma, and penetrate through the tissues until they reach the
The lowest great division of the Animal Kingdom. These animals are
composed of a gelatinous material, and show scarcely any trace of
distinct organs. The Infusoria, Foraminifera, and Sponges, with some
other forms, belong to this division.
PUPĘ). The second stage in the development of an Insect, from which
it emerges in the perfect (winged) reproductive form. In most insects
the pupal stage is passed in perfect repose. The chrysalis
is the pupal state of butterflies.
Backward development. When an animal, as it approaches maturity,
becomes less perfectly organised than might be expected from its early
stages and known relationships, it is said to undergo a retrograde
development or metamorphosis.
A class of lowly organised animals (protozoa), having a gelatinous
body, the surface of which can be protruded in the form of root-like
processes or filaments, which serve for locomotion and the prehension of
food. The most important order is that of the Foraminifera.
The gnawing Mammalia, such as the Rats, Rabbits, and Squirrels. They
are especially characterised by the possession of a single pair of
chisel-like cutting teeth in each jaw, between which and the grinding
teeth there is a great gap.
The male organs of flowering plants, standing in a circle within the
petals. They usually consist of a filament and an anther, the anther
being the essential part in which the pollen, or fecundating dust, is
A peculiar group of extinct Crustaceans, somewhat resembling the
Woodlice in external form, and, like some of them, capable of rolling
themselves up into a ball. Their remains are found only in the Palęozoic
rocks, and most abundantly in those of Silurian age.
An order of plants in which the flowers, which contain five stamens
and a pistil with two styles, are supported upon footstalks which spring
from the top of the flower stem and spread out like the wires of an
umbrella, so as to bring all the flowers in the same head (umbel)
nearly to the same level. (Examples, Parsley and Carrot).
The highest division of the animal kingdom, so called from the
presence in most cases of a backbone composed of numerous joints or
vertebroe, which constitutes the centre of the skeleton and at the
same time supports and protects the central parts of the nervous system.
In many of the lower animals (such as the Corals, Medusę, &c.)
reproduction takes place in two ways, namely, by means of eggs and by a
process of budding with or without separation from the parent of the
product of the latter, which is often very different from that of the
egg. The individuality of the species is represented by the whole of the
form produced between two sexual reproductions; and these forms, which
are apparently individual animals, have been called zooids.