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J 24 DESIGN IN NATURE<br />
species are known—one of which (M. electricus) is met with on the Nile. They grow to four feet or thereby. 1 had<br />
an opportunity of studying some fine specimens of the electric fish of the Nile at the Gezireh Aquarium Cairo<br />
(1904-5) and on one occasion, very many years ago, I received, at Edinburgh University, an electric shock trom<br />
an electric fish from Old Calabar. It sufficed to excite the Calabar specimen slightly, and to put one s hand into<br />
the water in which it was swimming, whereupon one or more very distinct shocks would be felt, and, once telt,<br />
could never be forgotten.<br />
.^ i. i. i. j„ oil r^^roT tha<br />
In the electric sheath-fish, the electric organ is not confined to one particular part, but extends all over the<br />
body beinc. most developed in the abdomen. It is contained between two aponeurotic membranes beneath the<br />
skin and is composed of rhomboidal cells which contain a gelatinous substance of rather firm consistence The<br />
nerve distributed to the organ forms an outstanding feature of the arrangement It has its ongin<br />
^-^^^^^f^^^<br />
has no connection with nerve ganglia, and consists of a single enormously developed nerve trunk. In this i differs<br />
materially from the arrangement met with in the electric eel, where more than 200 separate nerves are distnbuted<br />
to the electric organ. •<br />
, . > r ^ i a<br />
t+ „++„;„„ +^<br />
The greatest of the electric fishes is the electric eel {Gymnotus electricus) of tropical America. It attains to<br />
as much as six feet in length, and, according to the famous traveller, Humboldt, is dangerous to man and beast.<br />
It occurs in great plenty in Brazil and the Guayanas.<br />
The astounding feature in the electric organs of the gymnotus is their enormous nerve supply. More than<br />
200 nerves are distributed to the organs, and the nerves are very much larger than the sensory and motor nerves<br />
going to other parts of the body. As the electrical organs are special, so, in a large measure, are the nerves distri-<br />
buted to them The nerve supply consists of continuations of the anterior branches of the spinal nerves. They<br />
furnish branches not only to the electric organs but also to the skin and muscles of the back of the gymnotus. _<br />
The electric organs take the form of two pairs of longitudinal bodies ; the one pair situated between the skm<br />
and muscles on the back of the tail, the other pair between the skin and muscles along the anal fin. They have an<br />
involved and intricate structure, consisting as they do of a numerous series of perpendicular and transverse septa, m<br />
the interstices of which are imbedded prismatic cells containing a gelatinous substance. The septa are separated<br />
from each other by about the thirtieth of an inch, measure an inch in length, and contain some 240 cells, which secure<br />
for the electric organs a simply enormous surface.<br />
It is difiicult to reahse how intimately related the electric organs of fishes are to those of ordinary electric<br />
batteries, and how certain fiving creatures should have been provided with an apparatus for manufacturing, storing,<br />
and discharging electricity, giving them a power over their victims, or mayhap enemies, not possessed by even<br />
man himself.<br />
The electric organs of fishes can only be regarded as special creations, as the sense organs are. It is incon-<br />
ceivable that they could have been evolved from any living structure in the remote past, or that they could have<br />
been produced by natural selection, into which the elements of chance and utihty enter. The electric organs are<br />
massive and heavy, and, while they are eminently serviceable, when fully developed, to the electric fishes possessing<br />
them, no fish or series of fishes throughout the ages could have been burdened by them while undergoing a slow<br />
process of evolution, and while they were totally unfit for work of any kind. Mr. Darwin was wholly unable to<br />
explain their existence, and keenly felt the strain they put on his theory of " natural selection." Indeed he is<br />
said to have experienced a cold shiver whenever confronted with what, to him, was an insuperable difficulty.<br />
§ 30. Lines of Communication and Force, Nervous and Otherwise.<br />
Every one who has studied vital manifestations must have been struck with the fact that in plants and<br />
animals—the simplest as well as the most complex—there are means of communication as between their several parts<br />
and particles, and as between each individual organism and the physical universe. In other words, there is a means<br />
of communication between the atoms and molecules of the cells and tissues of plants and animals on the one hand,<br />
and between the individuals themselves and their surroundings or environment on the other.<br />
The lines of communication in the lowest plants and animals are by no means well defined. Thus in the cell<br />
plants and animals—the yeast plant and amoeba, for example—where there is little differentiation, and where there<br />
is, so to speak, a common structure and a common function, every part of the individual seems capable of transmitting<br />
impulses either from within or from without. In these cases, the living mass is endowed with a power which<br />
enables it to grow, divide, reproduce itself, and move. Every part reacts upon every other part, and all are under<br />
the influence of life and vital and physical force. Every part of the individual displays a low form of sensitiveness<br />
or its equivalent, and this in turn involves a rudimentary form of cognition and consciousness. The sensitiveness<br />
connects the several parts of the individual with each other, and the individual as a whole with its surroundings.