The Fly-shaker Muscle.

The panniculus carnosus, of which the facial muscles are part, is a great system of musculature found in various animal forms, and it furnishes a field for study of the evolution of the indifferent and the initial stages of the formation of a muscle. This is a servant of the brain in a more indirect manner than the facial muscles, but it, too, arises in obedience to the integrative action of the brain. The early specialisa­tion of it need not be considered here. It may be considered unwarrantable to claim the great Fly-shaker muscle of Ungulates as an indifferent structure, but the arguments by which the Pan-Selectionist would annex it to his sceptre, as a triumph of the minute care of the organism by selection, rest only on the assump­tion that he knows how it has become an adapta­tion to the life of its possessors. This is now more than it used to be a matter of opinion since the publica­tion of Professor Bateson’s revolutionary Materials, and others beside he have reserved to themselves the liberty of doubting the accepted explanations by the tangled path of adapta­tion. The statement of Weismann, “Everything is adapted in animated nature” was necessary to his theory of germinal selection, but it admits of extensive and numerous exceptions in view of the fact that so much of adapta­tion is partial and imperfect. If he had said that every organism as a being is adapted he would have been nearer the truth, but that every tissue and part of an organism is adapted is demonstrably untrue. A large number of organisms, themselves apparently well adapted, flourish well enough and reproduce their kind in spite of faulty and rudimentary tissues and parts. If it were not so we should have seen little of progress except what come under the laws of genetics,—a distributional matter. Even the super-Geddes could not distribute what was not there, for he could not deal with raw materials and change them by a fairy wand into manufactured articles. In the great field of domesticated plants and animals man has to find not only some mutation or some dominant strain and breed it to his will, but to cultivate the domestic qualities of animals and employ cultural conditions for plants. There is doubt expressed as to the length of time or numbers of generations during which these cultural conditions can extend, but Professor Thiselton Dyer many years ago made the remarkable statement as to plants:—“While specific stability under constant conditions appears to be the rule in nature, it is widely different in cultiva­tion. When a plant is brought under cultural conditions it maintains its type for some time unaltered, then gives way and becomes practically plastic. From my experience at Kew, where I saw the process continually going on, I hazarded the generalisa­tion that any species, annually reproduced from seed, could be broken down in five years. During that period specific stability, though menaced, tends to maintain itself. Darwin was well aware of this.”[76]

Most biologists from time to time betray the fact that their minds can only be relieved from an intolerable burden, in accounting for the numberless adaptations in organisms, by the view that many of them originate through factors of use and stimuli from environment, and at first are entirely indifferent as regards the survival or better mating of their possessors. To which the stern opponent replies, “What is there to show that in the existing scheme of things there is any provision made which will minister relief to the burden of your little mind?” To which, “answer came there none,” except a subdued reflec­tion that everything we see of living, striving nature around us has a most provoking way of speaking to us of daily, hourly and incessant action and reaction, stimulus and response, and that those who view the process thus do seem to bring some order into what would otherwise be chaos—and yet all the while someone is being grossly deceived! This “may be magnificent but it is not proof,” some will say, and will ask if the older observers of the heavenly bodies were not wrong in their complete convic­tion that the sun went round the earth. This digression introduces the role of the fly-shaker. If I am told that this muscular sheet in a cow or horse to-day is a relic of raw material inherited from a remote ungulate stock little evolved, and that it contributes in hot weather in the time of flies to the comfort and better mental state of the cow or horse, that it shall be able to keep those enemies at bay, and that the muscle is kept well in order by two or three months’ practice in each year I can understand in a measure its presence to-day. It has an efficient ally in the sweeping tail of a cow and that of a wild horse, and both of these weapons are further aided by the mobile ears of cow and horse, and the stretching movements of its head and neck. Thus the body of a cow, for example, is like a map with four territories delimited, that of the fly-shaker, the tail, the ears and the head and neck. Between these offensive weapons a cow is better defended against flies than a European in India by his punkah, or China was by its great wall, or Britain by the wall of Vallum of Hadrian or the wall of Severus, which with forts and garrisons was designed to protect it. Speaking in allegory the evolving brain of an early ungulate occupies the position of an ancient Chinese Emperor or a Roman Proconsul in Britain in its provision against “barbarians,” either Asiatic or Celtic. The resemblance goes further, for no experienced Roman General, whatever the Celestial minds in China may have thought, would fear that the loss of a sector of his wall would imperil the army of occupa­tion in Britain or the fabric of the Roman Empire. But as, in the long run it contributes to one’s welfare to be comfortable, and even the domestic ungulate is somewhat of a hedonist, a well-developed fly-shaker is maintained, the occasional use of which in winter and frequent use in summer and the active purposeful switching of tail, twitching of ears and jerking of head have their limited value. Here there is ample room for diverse opinion and the opponent will ask with some degree of force how we know that there is no more benefit to the cow from its fly-shaker than a mild degree of comfort, and may assert that the possession and use of it may have survival-value by its defence against deadly parasites. We do not know, nor does he, but it would seem that except for the tsetse fly in Africa the plague of flies does little to an ungulate beyond irritating its brain, and if he had no fly-shaker, he would still be able to reach a considerable distance with his tail, ears and head over the irritated regions. The question of survival indeed resolves itself into the vigour and energy of his integrating brain.

To this view of the function and origin of the panniculus carnosus the busy systematist and student of genetics may refuse to listen, and pass to the order of the day, but I submit that in stating a position it is useful to put forward a crude example in which the issue is plain, and which subsumes an immense number of smaller and more subtle cases, and in a region where the most hardy rebel will not dispute altogether the sway of personal selection. It is a question here of the manner in which, speaking in metaphor, the early ungulate first set about making his eolithic or palæolithic weapons and fashioned them into what we see to-day. “Forged by the incident of use” and habit meets the story of the fly-shaker far better than some mutation arising in far back ages or some dominant variation, or “useful variation within the germ.” At any rate Lamarck finds the raw material to hand, and there are supplied adequate noci-cipient stimuli with response, in regions where these are most active under the dominating action of the brain.