WAYS AND MEANS OF LIVING

WAYS AND MEANS OF LIVING
IN our hunàan society each individual must obtain the things necessary for existence; the manner by which he acquires them, whether by one trade or another, by this means or by that, does hOt physica]ly matter so long as he provides himself and his family with food, clothing, and shelter. Exactly so it is wita all forms of lire. The physical demands of living matter make certain things necessary for the maintenance of lire in that matter, but nature has no law specifying that any necessity shall be acquired in a certain manner. Lire itself is a circum- scribed thing, but it bas complete freedom of choice in the ways and means of living. It is useless to attempt to make a definition of what living matter is, or ofhow it differs from non-living matter, for all definitions have failed to distinguish animate from non-animate substance. But we all know that living things are distinguishable from ordinary non-living things by the fact that they make some kind of response to changes in the contact between themselves and their environment. The "environment," of course, must be broadly inter- preted. Biologically, it includes all things and forces that m any way touch upon living matter. Not only bas every plant and animal as a whole its environment, but every part of it has an environment. The cells of an animal's stomach, for example, have their environment in the blood and lymph on one side, the contents of the stomach on the other; in the energy of the nerves distributed to them; and in the effects of heat and cold that penetrate them.
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The environmental conditions of the life of cells in a complex animal are too complicated for an elemental study; the elements of lire and its basic necessities are bet- ter understood in a simple organism, or in a one-celled animal; but for purposes of description, it is most con- venient to speak of the properties of mere protoplasm. AIl the vital needs of the most highly organized animal are .pr.esent in any part of the protoplasmic substance of which t ,s composed. Protoplasm is a chemical substance, or group of sub- stances, the structure of which is very comp]ex but is main- tained so long as there is no disturbance in the environ-
'°- ° BCIs BCIs BC]s A ]3 C FIG. 6. Diagram show]ng the relation of the germ ce]ls (GCIs) and the body cells (BCIs) in successive generations A fertilized germ cell of generation A forms the germ cells and by cells of B, a fert]lized germ cell of B forms the germ cells and by cells of C, and so on. The offspring C of B derives nothing from the body cells of the parent B, but both offsp6ng C and parent B have a oemmon origin in a germ cell of A
metat. Let some least thing happen, however, such as a change in the temperature, in the strength of the light, in the weight of pressure, or in the chemical composition of the surrounding medium, and the protoplasmic molecules, in the presence ofoxygen, are likely to have the balance of their constituent particles upset, whereupon they partly decompose by the union of their less stable elements with oxygen to form simpler and more permanent compounds. The decomposition of the protoplasmic substances, like all processes of decomposition, liberates a certain amount of energy that had been stored in the making of the molecule, and this energy may manifest itselfin various ways. Ifit
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WAYS AND MEANS OF LIVING
takes the form of a change of shape in the protoplasmic mass, or movement, we say the mass exhibits signs of life. The state of being alive, however, is more truly shown if the act can be repeated, for the essential property of living matter is its power of reverting to its former chemical composition, and its ability thus gained of again reacting to another change in the environment. In restoring its lost elements, it must get these elements anew from the environment, for it can not take them back from the sub- stances that have been lost. Here, expressed in its lowest terres, is the riddle of the physical basis of lire and of the incentive to evolution in the forms of lire. Not that these mvsteries are any more easily understood for being thus analyzed, but they are more nearly comprehended. Being alive is maintaining the power of repeating an action; it involves sensitivity to stimuli, the constant presence of free oxygen, elimination of waste, and a supply of substances from which carbon, hydrogen, nitrogen, and oxygen, or other necessary ele- ments, are readily available for replacement purposes. Evolution results from the continual effort of living matter to perform its lire processes in a more efficient manner, and the different groups of living things are the result of the different methods that lire has tried and found advan- tageous for accolnplishing its ends. Living organisms are machines that have become more and more complex in structure, but always for doing the same things. If animals may be compared with machines in their physical mechanim, they are like them, too, in the fact that they wear out and are at last beyond repair. But here the simile ends, for when your car will no longer run, you must go to the dealer and order a new one. Nature provides continuous service by a much better scheme, for each organism is responsible for its own successor. This phase of lire, the replacement of individuals, opens another subject involving ways and means, and it, likewise, can be understood best in its simpler manifestations.
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INSECTS
The facts of reproduction in animais are not well ex- pressed by our name for them. Instead of "reproduc- tion," it would be-truer to say "repeated production," for individuals do not literally reproduce themselves. Genera- tions are serially related, not each to the preceding; they follow one another as do the buds along the twig of a tree,
Flç. 6 3. The external structure of an insect The body of a grasshopper dissected showing the head (H), the thorax and the abdomen (.4b). The head carries the eyes (E), the antennae (,llnt), and the mouth parts, which include the labrum (Lrn), the mandibles (Md), the maxillae {Mx), and the labium (Lb). The thorax consists of three segments {I, 2,), the flrst separate and carrying the first legs (L,), the other two com- bined and carrying the wings (1¢', 11"), and the second and third legs (L,, L.). The abdomen consists of a series of segments; that of the grasshopper bas a large tympanal organ (Tre), probably an ear, on each side of its base. The end of the abdomen carries the external organs of reproduction and egg-laying
and buds on the same twig are identical or nearly so, not because one produces the next, but because all are the result of the same generative forces in the twig. If the spaces of the twig between the buds were shortened until
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one bud became contiguous with the one before, or became enveloped by it, a relation would be established between the two buds similar to that which exists between succes- sive generations of lire forms. The so-called parent gen-
eration, in other words, contains the germs of the succeeding generation, but it does not produce them. Each generation is simply the custodian of the germ cells entrust- ed to i t, and the "off- spring" resembles the parent, not because it is a chip off the parental block, but because both parent and offspring are developed from the same line of germ cells. Parents create the conditions under wli, ch the germ cells will de- velop; they nourish and protect them during the period of their develop- ment; and, when each generation has served the purpose of its ex- istence, it sooner or later dies. But the in- dividuals produced from
F,c. 64. The leg of a young grasshopper, showing the typical segmentation of an insect's leg The leg is supported on a pleural plate (Pi) in the lateral wall of its segment. The basal segment of the free part of the leg is the coxa (Cx), then comes a small trochanter (Tf), next a long femur (F) separated by the knee bend from the tibia (Tb), and lastly the foot, consisting of a sub-segmented tarsus (Tar), and a pair of terminal claws (CI) with an ad- hesive lobe hetween them
its germ cells do the same
for another set of germ cells produced simultaneously with themselves, and so on as long as the species persists. To express the facts of succession in each specific form of animal, then, we should analyze each generation into germ cells and an accompanying mass of protective cells which
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forms a body, or soma, the so-called parent. Both the body, or somatic, cells and the germ cells are formed from a single primary cell, which, of course, is usually produced by the union of two incomplete germ cells, a spermatozoon and an egg. The primary germ cell divides, the daughter cells divide, the cells of this division again divide, and the division continues indefinitely until a mass of cells is pro- duced. At a very early stage of division, however, two groups of cells are set apart, one representing the germ cells, the other the somatic cells. The former refrain from further development at this time; the latter proceed to build up the body of the parent. The relation of the somatic cells to the germ cells may be represented diagram- matically as in Figure 62, except that the usual dual par- enrage and the union of germ cells is not expressed. The sexual form of reproduction is not necessary with all lower animals, nor with all generations of plants; in some insects the eggs can develop without fertilization. The fully-developed mass of somatic cells, whose real function is that of a servant to the germ cells, has assumed such an importance, as public servants are prone to do, that we ordinarily think of it, the body, the active sentient animal, as the essential thing. This attitude on our part is natural, for we, ourselves, are highly organized masses of somatic cells. From a cosmic standpoint, however, no creature is important. Species of animais and plants exist because they have found ways and means of living that have allowed them to survive, but the physical universe cares nothing about them--the sunshine is hOt made for them, the winds are not tempered to suit their conven- ience. Life must accept what it finds and make the best of it, and the question of how best to further its own wel- fare is the problem that conffonts every species. The sciences of anatomy and physiology are a study of the methods by which the soma, or body, bas contrived to meet the requirements imposed upon it by the unchanging laws of the physical universe. The methods adopted are as
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numerous as the species of plants and animais that have existed since lire began. A treatise on entomology, there- fore, is an account of the ways and means of living that insects have adopted and perfected in their somatic organ- ization. Before discussing insects in particular, however, we must understand a little more fully the principal con-
ditions of living that na- ture places on all forms of lire. As we have seen, lire is a series of chemical re- actions in a particular kind of matter that can carry on these reactions. A "reaction" is an action; and every act of living matter involves a break- ing down of some of the substances in the proto- plasm, the discharging of the waste materials, and the acquisition of new materia]s to replace those lost. The reaction is in- herent in the physical or chemical properties of protoplasmic compounds and depends upon the substances with which the protoplasm is sur- rounded. It is the func-
Tb
.'Fb :!ïllen
Fm. 6 5. Legs of a honeybee, showing special modifications A, outer surface of a hind leg, with a pollen basket on the tibia (Tb) loaded with pollen. B, a fore leg, showing the antenna cleaner (a) between the tibia and the tarsus, and the long, halry basal segment of the tarsus (t Tar), which is used as a brush for cleaning the body
tion of the creature's mechanism to see that the con- ditions surrounding its living cells are right for the con- tinuance of the cell reactlons. Each cell must be provided with the means of eliminating waste material and of restoring its lost material, since it can not utilize that which it has discarded.
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With the conditions of living granted, however, proto- plasm is still only potentially alive, for there is yet required a stimulus to set it into activity. The stimulus for lire activities comes from changes in the physical forms of energy that surround or infringe upon the potentially living substance; for, "live" matter, like all other matter, is subject to the law of inertia, which decrees that it must remain at rest until motion is imparted to it by other
E
FIO. 66. The head and mouth parts of a grasshopper A, facial view of the head, showing the positions of the antennae (dnt), the large cornpound eyes (E), the slrnple eyes, or ocelli (O), the broad front lip, or labrum (Lin) suspended from the cranium by the clypeus (Clp), and the bases of the mandibles (Md, Md) closed behind the labrum B, the rnouth parts separated from the head in relative positions, seen from in front: Hphy, hypopharynx, or tongue, attached to base of labiurn; Lb, labiuml Lin, labrum; Md, mandibles; Mx, maxillae
motion. A very small degree of stimulating energy, how- ever, may result in the release of a great quantity of stored energy. The food of all living matter must contain carbon, hydrogen, nitrogen, and oxygen. The mechanism of plants enables them to take these elements from com- pounds dissolved in the water of the soli. Animais must get them from other living things, or from the products of
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living things. Therefore, animals principally have de- veloped the power of movement; they have acquired grasp- ing organs of some sort, a mouth, and an alimentary canal for holding the food when once obtained. In the insects, the locomotory function is subserved by the legs and by the wings. Since all these organs, the three pairs of legs and the two pairs of wings, are carried by the thorax (Fig. 63, Th), this region of the body is distinctly the locomotor center of the insect. The legs (Fig. 64) are adapted, by modifications of structure in different species, for walking, running, leaping, digging, climbing, swim- ming, and for many varieties of each of these ways of pro- gression, fitting each species for its particular mode of living and of obtaining its food. The wings of insects are important accesslons to their locomotory equipment, since they greatly increase their means of getting about, and thereby extend their range of feeding. The legs, fur- thermore, are often modified in special ways to perform some function accessory to feeding. The honeybee, as is well known, has pollen-collecting brushes on its front legs (Fig. 65 B), and pollen-carrying baskets on its hind legs (A). The mantis, which captures other insects and eats them alive, bas its front legs made over into those efficient organs for grasping its prey and for holding the struggling victim which have already been described (Fig. 46). The principal organs by which insects obtain and ma- nipulate their food consist )f a set of appendages situated on the head in the neighborhood of the mouth, which, in their essential structure, are of the nature of the legs, for insects have no jaws comparable with those of vertebrate animais. The mouth appendages, or mouth parts as they are called, are very different in form in the various groups of insects that have different feeding habits, but in all cases they consist of the same fundamental pieces. Most important is a pair of jawlike appendages, known as the mandibles (Fig. 66 B, Md), placed at the sides of the mouth (A, Md), where they swing sidewise and close upon each other
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