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126 DESIGN IN NATURE<br />
of origin of the individual or with a centre developed during the process of differentiation. The ovum is the centre<br />
of the developing foetus—the brain is the centre or terminal of the adult vertebrate animal.<br />
While the shape of the plant and animal is determined to a large extent by the hues of communication and<br />
force, the latter in turn are dominated within Umits by the former. Thus, in rod-Uke plants and animals the lines<br />
of communication and the direction of force are in straight lines ; in globular plants and animals with a central<br />
origin they are in straight lines and in curves, whereas in spiral plants and animals they are helical.<br />
In plants and in the lowest animals there is no trace of a nervous system as we know it, but a nervous system<br />
or its equivalent may nevertheless exist in both in an undifferentiated form. The fact that some of the lowest<br />
animals—the amoeba for instance, and certain of the higher plants, such as the sundew—can, and do, move in given<br />
directions, at certain times, and to definite ends, goes far to prove not only that there are lines of communication<br />
akin to nerve tracts, but that there are also controlhng forces which move along these Hues, resembling in many<br />
respects nerve forces.<br />
To trace the rise and progress of the nervous system in animals to its culmination in man is one of the most<br />
difficult problems in physiology. Animals which were long supposed to be devoid of a nervous system (the jelly-<br />
fish for example) are now known to possess it. The nerves in the jelly-fish are not only extremely delicate, but they<br />
are also very soft. The condition of fluidity or softness is characteristic even of the human brain, which is the<br />
highest representative of nerve substance. The brain, which transcends all other organs in power, is, strange to say,<br />
nine-tenths water. A Uttle excess of softness in the nervous system of the jelly-fish would make the nerves so<br />
transparent as to be invisible. It follows from this that a fluid or semi-fluid nervous system in animals, and even in<br />
plants, is well within the possibihties. Certainly the movements and simultaneous power of feehng possessed by<br />
certain plants, and the majority of even the lowest animals, plainly indicate some such arrangements.<br />
If any one takes the trouble to study under the microscope the countless myriads of animalcules and low animal<br />
and vegetable forms which swarm in water and Uquid generally, and if, in particular, he watches how in their<br />
darting about in search of food they regulate their speed, the direction in which they move, and, in especial, how<br />
they avoid colliding with each other, he will be forced to admit that none of the movements he observes are chance<br />
movements. If this be conceded, then the obvious corollary is that the movements referred to are voluntary. Volun-<br />
tary movements, however, as we know them, imply a nervous system, or its equivalent, and this in turn necessitates<br />
sensitiveness of a kind. Sensitiveness implies feeling, and feehng cognition, which culminates in the consciousness<br />
of the higher animals. The most complex structures are, at their beginnings, developed from comparatively simple<br />
and very slightly differentiated protoplasm. In plants and the lowest animals, if nerve substance exists, it must<br />
occur in a fluid or semi-fluid, transparent state. The semi-liquid condition of nerve matter in the jelly-fish favours<br />
this view. Living things are not chance products. They are, on the contrary, distinct entities. From the lowest<br />
to the highest they have independent roles to perform, and they perform them with remarkable regularity and<br />
uniformity. In order to do so, they must be provided with bodies in the form of living matter, and these bodies<br />
must be amenable to control as regards the intake and output of food, as regards respiration, circulation, sensation,<br />
movement, excretion, &c. ; but control imphes directly or indirectly the possession of a nervous system, or its<br />
equivalent in an undifferentiated or invisible form. This argument is valid as regards the entire race of animals.<br />
It also apphes, within limits, to quite a large number of plants.<br />
Founding as we do our ideas of sensation, perception, movement, &c., on a brain, sensory and motor nerves,<br />
muscles, &c., as we find them in the higher animals, we are apt to deny to the lower and lowest animals, even in<br />
a rudimentary form, the structures and attributes which we find in a greater or lesser degree of perfection in the<br />
higher and highest animals. Nothing could be more unphilosophical. Brain and nerve substance and muscle as<br />
mere hving matter, have not necessarily any advantage over other living matter, and there can scarcely be a<br />
doubt that in all living matter, even in protoplasm, there are the potentialities and powers which lend themselves<br />
to the formation at once of the simplest and most complex plant and animal organisms. These organisms, the<br />
simplest equally with the most complex, are independent beings, capable of managing their o^vn affairs, each in its<br />
own way. If the most complex exercise their functions through the instrumentahty of a brain, nervous svstem and<br />
muscles, that is no reason why the more simple should not exercise similar functions by other means and methods<br />
or by similar means and methods in what appears to us (with our hmited powers of observation) an undifferentiated<br />
form. To take an example. The vacuoles in certain water plants exhibit rhythmic movements in every respect<br />
similar to those displayed by the mammalian heart ; the vacuoles closing suddenly and opening slowly, as in the<br />
several' compartments of the heart. But plants have neither muscles nor nerves in the ordinary sense. Again<br />
the heart of the chick, while yet a mass of nucleated cells, and before it even contains blood, displays characteristic<br />
rhythmic movements. Here again the muscles and nerves to which we attribute the rhythmic movements of the<br />
adult heart are absent.