Page:Popular Science Monthly Volume 7.djvu/61

Rh ; the after-part of the divided body also moves on, but only in obedience to its own ganglionic centres, and without any guidance from, or relation to, the sensorium, or the anterior portion of the body.

Thus we see the ordinary movements of the animal continuing to be repeated with only that part of the nervous system in operation which is capable of producing reflex action. What the entire creature has been accustomed to do, the separate parts continue to do when cut off from the guiding influence of the sensorium. The same holds good even in some of the more highly-organized, members of the articulate series. A remarkable instance is given by Dr. Carpenter, as shown in the mantis, an insect allied to the crickets, which performs its accustomed and very peculiar actions not only when the head is removed, but the segments of the body perform each its accustomed part, and no other, when the body itself is divided. So also a certain kind of water-beetle, after the sensorium is removed, remains motionless so long as it rests upon a dry surface; but, being placed upon the water, its accustomed element and stimulus, performs its accustomed movements of swimming, and with such energy as to strike aside its companions with great violence. These motions, which are repeated, as has been seen, under the influence of the ganglionic system alone, and by the simple process of reflex action, are termed automatic; and when these actions, though often more complex and varied, are repeated in the same automatic manner under the guidance of the sensorium, and under the stimulus derived from sensation, they are called instinctive.

Coming, now, to the higher species of articulates, we find the so-called social insects, and especially bees, furnishing the most wonderful examples of instinctive action; they construct for themselves habitations, some of them involving nice principles of geometry; they store up food for future use, and their whole economy seems, at first glance, to demand the presence and aid of even a rare intelligence; yet, on examination, it is found that no teaching is required, no thought nor memory is brought into use in these remarkable actions, but each insect goes to work without direction and without individual experience, and does at once, without hesitation, the first time as well as ever, that which is in its nature to do. "It acts according to its nervous organization."

How the insect comes by this impulse to do, is one of those seemingly simple questions which, in reality, includes the whole; it is the ever-recurring question regarding each new faculty as it makes its appearance in the series, and demands a few words in reference to the main theories involved. The term instinct is not to be taken, in its popular sense, as referring to all the actions performed by animals in distinction from those performed by man, but must be limited to those automatic actions which are performed without teaching or individual experience. Now this impulse, or instinct, as exemplified in the bee,