flying, long-lived, and hence more exposed females, as compared with the lighter, swifter, short-lived males.

It has been found that individuals of a single species may mimic several different species of defended insects, this polymorphism of pattern existing in different localities, or indeed in a single one. Marshall believes that seasonal polychromatism of certain butterfly species is associated with the mimicry of certain defended butterflies of different species, these different species appearing at different times of the year.

It is needless to say that such hypotheses and theories of the utility of color and pattern have been subjected to much criticism, both adverse and favorable. The necessity for limiting results within the working range of efficient causes has been the soundest basis, in our judgment, for the adverse criticism of the theories of special protective resemblance, warning colors, and mimicry. Until recently most of the observations on which the theories are based have been simply observations proving the existence of remarkable similarities in appearance or equally striking contrasts and bizarrerie. The usefulness of these similarities and contrasts had been deduced logically. but not proved experimentally nor by direct observation. recent years, however, a much sounder basis for these theories has been laid by experimental work. There is now on record a large amount of strong evidence for the validity of the hypothesis of mimicry. Certainly no other hypothesis of equal validity with that of protective resemblance and mimicry has been proposed to explain the numerous striking cases of similarity and the significant conditions of life accompanying the existence of these cases, which have been recorded as the result of much laborious and indefatigable study by certain naturalists.

Plateau and Wheeler have tasted so-called inedible and distasteful insects and found nothing particularly disagreeable about them. But as Poulton suggests, the question is not as to the palate of Plateau and Wheeler nor of any man; it concerns the taste of birds, lizards, etc. Better evidence is that afforded by actual observation of feeding birds and lizards; of experimental offering under natural conditions of alleged distasteful insects to their natural enemies. Marshall's observations and experiments on the point are suggestive and undoubtedly reliable. Much more work of the same kind is needed.

The efficient cause for bringing color and pattern up to such

a high degree of specialization has been assumed, by nearly all upholders of the use hypotheses, to be natural selection. This agent can account for purposefulness, which is obviously an inherent part of all the hypotheses. And no other suggested agent can. Weismann makes, indeed, of this fact, by inverting the problem, one of the most effective arguments for the potency and "Allmacht" of natural selection. He declares that the existence of special protective resemblance, warning colors, and mimicry proves the reality of selection. But it must be asked, while admitting the cogency of much of the argument for natural selection as the efficient cause of high specialization of color and pattern as we have seen it actually to exist, how such a condition as that shown by the mimicking viceroy butterfly has come to be gradually developed-gradual development being confessedly selection's only mode of working. Could the viceroy have had any protection for itself, any advantage at all, until it actually so nearly resembled the inedible monarch as to be mistaken for it? No slight tinge of brown on the black and white wings (the typical color scheme of the genus), no slight change of marking, would be of any service in making the viceroy a mimic of the monarch. The whole leap from typical Basilarchia to (apparently) typical Anosia had to be made practically at once. On the other hand, is it necessary for Kallima, the simulator of dead leaves, to go so far as it has in its modification? Such minute points of detail are there as will never be noted by bird or lizard. The simple necessity is the effect of a dead leaf; that is all. Kallima certainly does that and more. Kallima goes too far and proves too much. And there are other cases like it. Natural selection alone could never carry the simulation past the point of advantage.

But whatever other factors or agents have played a part in bringing about this specialization of color and pattern, exemplified by animals showing protective resemblances, warning colors, terrifying manners, and mimicry, natural selecti undoubtedly been the chief factor, and the basis the chief foundation, for the development of the : conditions.

CHAPTER XX

REFLEXES, INSTINCT, AND REASON

We live in a world which is full of misery and ignorance, and the plain duty of each and all of us is to try to make the little corner he can influence somewhat less miserable and somewhat less ignorant than it was before he entered it. To do this effectually it is necessary to be fully possessed of two beliefs-the first, that the order of nature is ascertainable by our faculties to an extent which is practically unlimited; the second, that our volition counts for something as a condition of the course of events.

Each of these beliefs can be verified experimentally as often as we like to try. Each, therefore, stands upon the strongest foundation upon which any belief can rest, and forms one of our highest truths. If we find that the ascertainment of the order of nature is facilitated by using one terminology or one set of symbols rather than another, it is our clear duty to use the former; and no harm can accrue so long as we bear in mind that we are dealing merely with terms and symbols.— HUXLEY.

ALL animals of whatever degree of organization show in life the quality of irritability or response to external stimulus. Contact with external things produces some effect on each of them, and this effect seems to be something more than the mere mechanical effect on the matter of which the animal is composed. In the one-celled animals, the functions of response to external stimulus are not localized. They are the property of any part of the protoplasm of the body. Just as breathing or digestion is a function of the whole cell, so are sensation and response in action. In the higher or many-celled animals each of these functions is specialized and localized. A certain set of cells is set apart for each function, and each organ or series of cells is released from all functions save its own.

In the more highly organized animals certain cells from the primitive external layer or ectoblast of the embryo are early set apart to record the relations of the creature to its environment. These cells are highly specialized, and while some of them are highly sensitive, others are adapted for carrying or transmitting the stimuli received by the sensitive cells, and still others have the function of receiving sense impressions and of translating them into impulses of motion. The nerve cells are receivers of impressions. These are gathered together in nerve masses or ganglia, the largest of these being known as the brain, the ganglia in general being known as nerve centers. The nerves are of two classes. The one class, called sensory nerves, extends from the skin or other organ of sensation to the nerve center. The nerves of the other class, motor nerves, carry impulses to motion.

The brain or other nerve center sits in darkness surrounded by protecting tissues or a protecting box of bone. To this brain, nerve center, or sensorium come the nerves from all parts of the body that have sensation-the external skin as well as the special organs of sight, hearing, taste, smell. With these come nerves bearing sensations of pain, temperature, muscular effortall kinds of sensation which the brain can receive. These nerves are the sole sources of knowledge to any animal organism. Whatever idea its brain may contain must be built up through these nerve impressions. The aggregate of these impressions constitutes the world as the organism knows it. All sensation is related to action. If an organism is not to act, it cannot feel, and the intensity of its feeling is related to its power to act.

These impressions brought to the brain by the sensory nerves represent in some degree the facts in the animal's environment. They teach something as to its food or its safety. The power of locomotion is characteristic of animals. If they move, their actions must depend on the indications carried to the nerve center from the outside; if they feed on living organisms, they must seek their food; if, as in many cases, other living organisms prey on them, they must bestir themselves to escape. The impulse of hunger on the one hand and of fear on the other are elemental. The sensorium receives an impression that food exists in a certain direction. At once an impulse to motion is sent out from it to the muscle necessary to move the body in that direction. In the higher animals

these movements are usually more rapid and more exact than with the lower forms. This is because the organs of sense and action, the sense cells, nerve fibers, and muscles are all highly specialized. In the starfish sensation is slight, nervous communication slow, and the muscular response sluggish, but the method is apparently the

13

14

10

12

FIG. 264.-Diagram showing how the

Protozoan, Oxytricha fallar, reacts to

cold; slide is heated at upper end and an Orytricha beginning at 1 continues

same.

But in recent years many biologists have come to believe that much of the behavior of the simplest animals, and some of the actions of the higher, are controlled in a more rigidly mechanical way than the above statements suggest; that, in a word, much of the action, and apparent instinctive or intelligent response of animals to external conditions, is an immediate physicochemical rather than vital phenomenon; that the animal body in its relation to the external world is much more like a passive, senseless, although very complex, machine, stimulated and controlled

to react by turning a little to right by external factors and con

and backing and advancing and repeatedly turning a little to right and

backing and advancing until position 14 is reached. (After Jennings.)

ditions, than like the percipient, determining, purposeful creature that our usual conception of the organism makes it out to be.

Clever experimenters, as Loeb, Lucas, Redl, Bethe, Uexkull, and numerous others, believe themselves justified in explaining a host of the simpler actions or modes of behavior of animals, on a thoroughly mechanical basis, as rigorous, inevitable reactions to the influence or stimulus of light, heat, contact, gravity, galvanism, etc. Phototropism, stereotropism, geotropism, etc., are the names given to these phenomena of response by action and behavior to stimuli of light, contact, and gravity respectively.

Some of these biologists are ready to carry their giving up