and spiders with their poor relations, the mites and tics, together with
the very peculiarly-shaped _Pycnogonida_ (which present us with a good
image of "no body"--being all legs and no body), and the singular
worm-like parasite _Linguatula_. Lastly, we come to the most
zoologically important and numerous of all the classes of
Arthropods--namely, to the "class" of insects--_Insecta_. Therein we
meet with the power of flight in its most perfect form--_i.e._, in the
Dragon-flies--and most of the species are aërial in their adult (or
_Imago_) condition. Some, however, are burrowers as, for example, the
mole-cricket--an insect which presents some curious analogies in
structure to the beast referred to in its name. Amongst insects may be
mentioned the most familiar of all, the House-fly (which belongs to the
order _Diptera_), and Beetles of all kinds (which constitute the order
_Coleoptera_), some of which latter are luminous, as is the well-known
glow-worm, and the exotic beetles _Pyrophorus_. Another order
(_Orthoptera_) is made up of the earwigs, cockroaches, crickets,
grass-hoppers, and their allies the locusts, with Bamboo-insects and the
curious walking-leaf (so-called from their resemblance to a Bamboo twig
and a foliage leaf respectively), the praying mantis, and other curious
kinds.
Bees and Ants, which belong to the order _Hymenoptera_, are, as every
one knows, celebrated for their wonderfully complex instincts and
community-life (which will occupy us later), and to the same order also
belong the Ichneumon insects, which are provided with long appendages at
the hinder ends of their bodies wherewith to pierce the bodies of
animals in order to deposit their eggs within them, or to pierce the
substance of plants, so producing "galls" which are structures of much
interest from several points of view.
Butterflies and Moths form another order of insects called
_Lepidoptera_, amongst which may be mentioned as (having to be referred
to hereafter) the true butterflies (_Papilio_), and the hawkmoths (some
of which in their flight so much resemble Humming-birds), the clear-wing
moths, and those moths the grubs of which are known as "silk-worms," and
certain moths of the genera _Solenobia_ and _Psyche_.
The numerous group of bugs is allied to the plant-lice (_Aphides_),
which so often infest our Pelargoniums when kept in dwelling-rooms.
Allied to them, again, are the small creatures the nature of which was
so long disputed, though familiar to commerce as "Cochineal." Really,
they are small, singularly inert, plant-lice, which adhere to the
surface of certain "Cacti."
The Dragon-flies, before referred to, are the types of the order
_Neuroptere_.
All the insects above mentioned, save the House-fly, have four wings, or
else none; but that familiar form may serve as the type of the
two-winged order (_Diptera_) to which belong all flies and
gnats--including, of course, the Mosquito--and the numerous "Bots," one
of which (the Tsee-Tsee fly) is so fatal to cattle in Africa.
Finally, amongst insects may be mentioned the wingless, but active order
of fleas (_Aphaniptera_), the wingless but sluggish lice (_Aptera_), and
the jumping and wingless springtails (_Thysanura_).
In leaving the class of insects, we leave all the more highly-organized
Invertebrata. But the next group to which we may direct our attention is
one which is exceedingly numerous, and contains a very varied assemblage
of forms. This group is the "sub-kingdom" of Worms, VERMES. First
amongst its contents may be mentioned the higher or true "worms," such
as the earth-worm (_Lumbricus_), the leech (_Hirudo_), the sea-mouse
(_Aphrodite_), and their allies, together with the worms which live in
tubes, which are called _Tubicolous_-"_Annelids_," because the whole
class of these higher worms bears the name _Annelida_.
In this connexion may be mentioned certain exceptional vermiform
creatures, about the affinities of which naturalists dispute.
One of these is a marine creature (called _Sagitta_, from the way in
which it shoots like an arrow through the water), which has many
affinities to Arthropods.
Another is a most remarkable worm, which has been found in the Bay of
Naples, and is called _Balanoglossus_. It is the type of a group called
_Enteropneusta_. To it reference will have again and again to be made on
account of certain singularities in its structure.
A very distinct class of creatures is termed _Bryozoa_ (or _Polyzoa_),
and is composed of very minute animals which live in compound
aggregations, and often grow up in an arborescent manner. The common
sea-mat (_Flustra_) is one example of the class, and another--a good
type--is called _Plumatella_. The _Bryozoa_ have many affinities with
the _Mollusca_, to which some naturalists consider them to belong.
Other worms form the class _Nematoidea_, of which many are parasitic and
many not so. Amongst the better known of the former may be mentioned the
worms which tease children (_Ascarides_), the guinea-worm (_Filaria_),
the scourge of Germans who eat raw meat (_Trichina_), the deadly
blood-parasite of the Nile (_Bilharzia_), and many others.
Another class (_Trematoda_) is made up of parasites called "Flukes," to
some of which (_e.g._, _Monostomum_) reference will have hereafter to be
made with respect to their processes of development.
The class _Turbellaria_ contains a variety of other worms of a lowly
kind, one or two of which (_e.g._, _Borlesia_) live coiled up in complex
tangles which, if unravelled, would attain a length of forty feet.
Amongst the commoner kinds may be mentioned the worm _Nemertes_, and all
worms called _Planariæ_ (which are mostly fresh-water, though some live
on land), allied to the flukes.
The class of tape-worms (_Cestoidea_) is one most numerous in its kinds,
which are all completely parasitic in habit. Some of them are so fatal
in their effects that they are estimated to occasion every seventh death
which occurs in Iceland, and they cause mortality amidst our own flocks,
producing in sheep the disease known as the "staggers."
Certain minute organisms, familiarly known as "Wheel-Animalcules," or
Rotifers, form the "class" _Rotifera_. They have gained their name
through an apparently (though, of course, not really) rotary motion, of
that end of their bodies at which the mouth is situated. Here also may
be mentioned certain curious aquatic worms called _Gasterotricha_, which
are closely allied to the wheel animalcules.
Finally may be mentioned the class _Gephyrea_, containing animals,
worm-like indeed in form, but which have much apparent affinity to the
group next to be spoken of--the group of star-fishes and their allies.
Amongst the _Gephyrea_ may be mentioned the worms called _Sipunculus_
and _Priapulus_.
This leads us to the sub-kingdom containing the star-fishes--the
sub-kingdom ECHINODERMA, which includes, besides the star-fishes (or
_Asteridea_), all sea-eggs or sea-urchins (_Echinidea_), the
brittle-stars _Ophiuridea_, as well as the elongated soft animals called
sea-cucumbers, or _Holothuridea_, some of which latter are known as the
Japanese edible, "Trepang."
Besides these groups there are still surviving a few creatures
(_Comatula_ and _Pentacrinus_) belonging to the class of "sea-lilies,"
or _Crinoidea_, creatures which once lived in countless multitudes, but
have now almost entirely passed away. All these crinoids were like
star-fishes on stalks, and of the existing forms, _Pentacrinus_ still
passes the whole of its life, and _Comatula_ its youth, in a stalked
condition.
The next great primary division, or sub-kingdom of animals, is
COELENTERA, and a good type of the coelenterates, the sea anemone
(_Actinia_), has now become a familiar object to us in our aquaria.
These animals are plant-animals, or zoophytes, and some of them build up
coral-reefs, or islands, and it is one kind which produces the red coral
of commerce. Forms essentially similar, but the solid supporting
framework of which is of a softer nature, are such as _Alcyonium_ and
_Pennatula_. All these belong to the "class" _Actinozoa_. There are
other coelenterates of an active free-swimming habit, such as _Beröe_
and _Cydippe_, which are balls of glassy transparency displaying
iridescent hues as they move rapidly through the water by means of their
peculiar locomotive organs.
Other coelenterates, of the same essential type but of simpler
structure, form the class _Hydrozoa_. Amongst these may be mentioned the
little _Hydra_ of our ponds, which will often come before us in our
survey of animal life. Some compound forms of Hydrozoa simulate the
compound Actinozoa; such are the calcareous millipores, and those with a
softer structure, called "corallines," such as _Eudendrium_ and many
others. The Portuguese man-of-war (_Physalia_) and the various forms of
jelly-fish (_Medusæ_) all belong to the _Hydrozoa_, as also does a very
curious and very elementary form, to which the name _Tetraplatia_ has
been given.
Next we come to the group of sponges, SPONGIDA, some of which--as the
now well-known _Euplectella_--are of marvellous beauty and delicacy of
structure; while others, as the sponge of commerce, are of much greater
simplicity of form. Simplest of all the sponges is the sponge called
_Ascetta Primordialis_. Some sponges have a horny, some a calcareous,
and some a siliceous skeleton, and (strange as it may appear) some have
a habit of boring into shells, and living in the excavations they make.
An animal recently discovered, _Dicyema_, may at this initial stage of
our inquiry be left with its place and affinities undetermined. It is a
minute worm-like creature of most exceptionally simple structure, which
lives parasitically within cuttle-fishes.
We now pass to animals (if so they are really to be considered) which
are the lowest and simplest of all, and which are mostly microscopic in
size, and may be grouped together under the term HYPOZOA, or under the
generally employed name _Protozoa_. With very few exceptions these
animals are aquatic, and if terrestrial they are found in damp
localities. Some are marine, others are fresh-water organisms.
The highest of the group are the animalcules, which are named
_Infusoria_, most of which are freely swimming organisms, though a
certain number of them live fixed to some supporting body.
Another group of _Hypozoa_ is that termed _Gregarinida_, a group made up
of very lowly parasites, such as are often found tenanting the
intestines of insects as well as those of higher animals. Finally, we
have the group of _Rhizopoda_, animals which have the faculty of
projecting and retracting (so to say, at will) filamentary or conical
processes of their semi-fluid substance, such processes being the
_Pseudopodia_, which were referred to earlier.[17]
Amongst the _Rhizopoda_, the most complex and beautiful are the delicate
and symmetrical creatures known as _Radiolaria_,[18] the siliceous
skeletons of which are amongst the most remarkable of microscopic
objects.
Allied to them are the simpler _Heliozoa_, of which the after-mentioned
_Actinophrys_ may be taken as a type.
Next come the _Flagellata_, or minute creatures which swim about by
means of one or two whip-like processes, whence the name of the group.
Last of all is the group of _Foraminifera_, animals which are well
worthy of note, seeing that, though they are each but as it were a
minute particle of structureless jelly, they manage to build most
complexly-formed, generally calcareous, shells, or to pick up from the
sand of the sea minute particles, which they agglutinate around them
with marvellous neatness and precision. Their calcareous shells are
generally pierced by a multitude of minute pores, through which the
little creatures protrude their _pseudopodia_. It is from these pores
(or _foramina_) that the group receives its name. All _Foraminifera_,
however, are not provided with shells. Some, as the _Amoeba_, are
naked, and the simplest of all animals, _Protogenes_ and _Protamoeba_,
consist of but a minute particle of semi-fluid jelly, or protoplasm,
naked and as devoid of every external protection as it is of internal
organization.
We have thus descended to the bottom of the animal kingdom, and passing
from these rudimentary forms, which are generally reckoned as animals,
we may next survey in ascending order the different organisms which
together compose the kingdom of Plants, a group much less rich in
species than is the animal kingdom.
At the bottom of that kingdom are very simple creatures, but little
different, to all appearance, from the lowest animals. As an example of
such we may take the minute plant _Protococcus_, which is an humble
member of the great group of _Algæ_, to which all sea-weeds belong. Not
all of this important tribe, however, are marine. Many are found in
fresh water--such as the protococcus itself, and many of the green
vegetable threads known as _Conferræ_. Some even live on land, and draw
their moisture from the atmosphere. The _Algæ_ are exceedingly varied in
their structure; some, like the protococcus, being of extreme
simplicity; others attaining a large size, and presenting the appearance
of a stout stem with branches and leaves.
The Algæ are divisible into the green-spored[19] (_Chlorospermeæ_), the
rose-spored (_Florideæ_), and the olive-spored (_Melanospermeæ_).
It is in the first division that the _Protococcus_ may be placed, as
also those microscopic plants called _Diatoms_ and _Desmids_. The
former, the _Diatomaceæ_, are a very numerous group of minute organisms,
some of which are used as test objects for microscopes. They contain in
their outer coat or case a relatively large portion of silex, and their
remains here and there form deposits--vast beds many feet in
thickness--known as "tripoli," and used for polishing. The minute
particle of their protoplasm is contained within the siliceous case.
They may be entirely free, or cohere in aggregations, or be attached to
a supporting surface by a slender stalk, which may ramify and bear a
little siliceous case or "frustule" at the end of each branch.
The desmids (or _Desmidiaceæ_) are green and devoid of silex, though
their protoplasm is enclosed in hard or flexible cases, often marked
with beautiful and characteristic patterns.
Both diatoms and desmids may cohere together, forming more complex
masses; but another creature allied to _Protococcus_ is noted for its
mode of cohesion. This is the microscopic plant _Volvox_, the
individuals of which cohere so as to form spheroidal aggregations, which
swim about by the action of filamentary prolongations of their
protoplasm, such prolongations reminding us of the pseudopodia of
radiolarians and other rhizopods.
Amongst these simplest plants may be also mentioned the curious
thread-like organisms, which, on account of their remarkable and as yet
unexplained movements, are called _Oscillatoriæ_.
Another curious vegetable organism which may here be mentioned is
_Vaucheria_. It is a green, thread-like plant, which may be several
inches long, and which at one stage of its existence (when it is what is
called a "spore") swims about by pseudopodial prolongations of its
protoplasm.
Some few of the _Chlorospermeæ_ are large and conspicuous organisms.
Such, _e.g._, is _Caulerpa_, which abounds on warm, sandy coasts, and on
which turtles browse. Though, as we shall hereafter see, it is really as
simple in structure as a particle of yeast, it yet presents a very
complicated external figure.
Some of the great group of _Algæ_ attain enormous dimensions. Thus,
_Macrocystis_ (one of the _Melanospermæ_), of the Southern Ocean, may be
even 700 feet in length. Another kind, _Lessonia_, forms submarine
forests, with stems like the trunks of trees.
The group of _Floridiæ_ includes the delicate and elegant sea-weeds,
which are amongst the most admired vegetable productions of our coasts.
They are of interest, on account of various peculiarities in their
reproductive processes.
Other lowly plants may, at least provisionally, be placed in the great
group to which mushrooms and truffles belong--the group of _Fungi_--a
group the members of which agree in certain exceptional phenomena of
function,[20] as well as of structure and composition--as they are
exceptionally nitrogenous.
Amongst the lowest which we may for convenience provisionally include in
this group may be mentioned minute _Vibrios_, such as the _Bacteria_ so
much talked of in connexion with spontaneous generation, and the small
plant which by its growth produces fermentation--the yeast-plant
(_Saccharomyces_).[21] Closely allied to the yeast-plant are the
"moulds" which grow on organic matters such as _Penicillium_, _Mucor_,
_Saprolegna_, _Phytophthora_, the last of which is the potato disease.
A singular group of organisms goes by the name of _Myxomycetes_. These
enigmatical creatures have been classed in turn as animals and as
plants, and, indeed, at one period of their existence they seem to have
more resemblance to the former, while at another stage of their life
history they must unquestionably be ranked as plants. When young, they
are in a semi-fluid condition, and so move that they seem, as it were,
to flow over the body on which they rest. They grow upon the bark of
trees or on leaves and decayed wood. They exhibit movements like those
of the amæbæ and are said to engulph nutritious matters which come in
their way.
The dry-looking, green, grey, red or yellow vegetable structures which
encrust our rocks, walls, and trees, and which are called _Lichens_,
form a group of plants curiously intermediate between Fungi and _Algæ_.
Plants somewhat higher in the scale of vegetable life are those which
are termed liverworts (_Hepaticæ_), including the scale-mosses
(_Jungermanniaceæ_) and _Marchantia_. These plants, as we shall see, are
interesting on account of the variations to be found in the forms of
different genera. In many, there is no stem, but only a connected series
of green disk-like expansions, while others have a distinct stem with
leaf-like outgrowths.
Two genera of aquatic plants (_Chara_ and _Nitella_) constitute another
group of plants called _Characeæ_. These will be hereafter referred to
both on account of peculiarities in their structure and on account of a
peculiar motion of protoplasm which is easily to be seen[22] in them.
Mosses (_Musci_) are familiar objects to every one in this country, and
allied to them are the so-called "club-mosses" or _Lycopods_, which form
a sort of green sward in so many parts of the warmer regions of the
earth. To one of the lycopods, called _Selaginella_, reference will
hereafter be made in connexion with its very instructive reproductive
process.
Certain humble plants, in some of which the foliage leaves present a
superficial resemblance to those of a four-leaved clover, are popularly
called pepperworts; by botanists, _Rhizocarpeæ_ or _Marsiliaceæ_. They
are creeping or floating stemless plants which inhabit ditches or
inundated places. They are scattered over both the Old and New Worlds,
but are chiefly found in temperate latitudes.
The horse-tails (_Equisetaceæ_) are also found in most parts of the
world, though wanting in Australia and New Zealand. They inhabit wet and
sandy places, and sometimes are of a considerable size even in the
present day, but in ancient geological periods they attained the
proportions of trees.
This group leads us on to their allies the ferns which form a very large
natural group _Filices_ or _Pteridophytes_--a group now familiar to
every one interested in plants. Common as ferns are in our own country,
they are far more abundant and attain to a much greater size in southern
latitudes--notably in New Zealand and various Pacific islands.
All the plants hitherto enumerated, from the protococcus to the
tree-ferns inclusive, together form what is commonly regarded as one
great primary division or "sub-kingdom" of vegetals called CRYPTOGAMIA.
In no plant belonging to this sub-kingdom--in no single cryptogam--is
any flower ever developed. These form the great group which is often
spoken of as "flowerless plants."
The other primary division of vegetable organisms consists of all plants
with flowers, and is termed PHANEROGAMIA, and is subdivided into two
sections,[23] very unequally numerous. To the first section of
phanerogams--a section containing comparatively few kinds--belong all
firs, pines, yews, junipers, araucarias, and a most remarkable African
plant, _Welwitschia_, which has never more than two leaves, though these
attain enormous dimensions. All these plants are collectively spoken of
as conifers, or _Coniferæ_. Besides these, certain curious southern
forms called Cycads are also associated in this section. To this
section, thus composed of conifers and cycads, the name GYMNOSPERMS is
given, from the naked mode of development of their young seeds. These
gymnosperms are also characterized by having such peculiar and
inconspicuous flowers that the ordinary observer would hardly apply that
term to denote their floral organs.
All the plants which yet remain to be noticed, and which belong to the
second and very much larger section of the PHANEROGAMIA are spoken of as
_Angiosperms_. Their seeds are, from their first appearance, in a very
different condition from those of gymnosperms, and their flowers are
generally conspicuous. To this group, therefore, belong all the familiar
ornamental plants of our gardens, and all the brightly coloured natural
ornaments of our fields, as well as a number of herbs and trees, the
flowers of which, though truly flowers, are not commonly recognized as
such.
This group of Angiospermous flowering plants is divided into a great
number of natural groups or "orders." Of these there are about 275, and
they are grouped in two sets or classes, which are separated one from
another, as we shall hereafter see, by differences as to their modes of
growth, the structure of their seeds, the numbers of the parts of their
flowers, and the course of the veins in their leaves.
First amongst the Angiospermous flowering plants may be mentioned the
grasses forming the order _Gramineæ_, including under that term the
tree-like bamboos (of multitudinous uses), with the rice plant, and all
the grain-bearing herbs, all of which are grasses. Thus, with much
reason may it be said of man, that "all flesh is grass;" for with the
exception of the piscivorous Esquimaux, the exclusively flesh-eating
Gouchos, the population of Australia, and the people of the Molluccas
who nourish themselves on sago--which is the produce of a palm--with
these and a few more exceptions, the staple food of the human race is
one or another form of grass. It is, indeed, a remarkable fact that men
of such varied races so widely spread should have thus selected as their
food objects so little tempting in appearance, and so small and so
inconspicuous as the seeds of grasses!
Allied to the grasses are the sedges (forming the order _Cyperaceæ_),
and the rushes (_Juncaceæ_). The apparently insignificant, but really
interesting duckweeds (_Pistiaceæ_) should also be noted with the
bullrushes (_Typheæ_), and the arums (_Aroideæ_). This last-mentioned
order, familiar to us by the kind known as "Lords and Ladies," presents
some climbing forms in tropical countries. Generally acrid, some
species, when in flower, even produce headache and vomiting; at least an
explorer was attacked with these symptoms after gathering forty
specimens of _Arum dracunculus_. The order is also interesting from
experiments as to vegetable heat, which have been made with the flowers
of some of its species.
The screw-pines (_Pandanaceæ_) are not "pines" at all, any more than
"pine-apples" are pines. They are, indeed, trees or shrubs, which, from
one point of view, may be regarded as gigantic bulrushes. The flowers of
certain species are in some places eaten as the solid equivalent of a
love potion. Allied to the plants of the last-mentioned order are the
palms (_Palmaceæ_), which are the first really large trees we come to
after leaving the tree-ferns and the gymnosperms. Amongst the more
noteworthy palms may be mentioned the palmetto (_Chamærops_) of Southern
Europe (a summer ornament of our public gardens), the date palm, the
areca palm, the sago palm, the cocoa palm, the rattan palm--a natural
cordage--and _Seaforthia_, so remarkable for its graceful and elegant
form.