Economic zoology : an introductory text-book in zoology, with special reference to its applications in agriculture, commerce, and medicine

Front matter

22101895339

THE MACMILLAN COMPANY

MACMILLAN & CO., Limited

Preface

The immense progress in recent years in the application of scientific knowledge concerning animals to the affairs of everyday life, the great extent to which animals and animal products enter into commerce, and the very vital relation that is now known to exist between various forms of life and the diseases affecting man and the domestic animals, seem to warrant a general text in zoology in which these phases of the subject are given more emphasis than has been the practice. Such a viewpoint has, moreover, the advantage of awaking an interest in the subject which, from a purely educational standpoint, is not to be overlooked. Interest is one of the prime factors in concentrated, effective study, and to know that the subject studied bears in an important way on life and prospective duties is no small element in successful study. It is the writer’s belief that such forms as the parasitic worms, trichina, earthworm, oyster, crayfish, grasshopper, mosquito, fish, or bird lose none of their scientific interest or value as disciplinary objects of study when their importance to human life is considered. On the contrary, his own experience leads him to believe that this viewpoint stimulates to more careful and effective study.

This book, however, is not intended merely as a text-book for the school or college student, but it is hoped that it may be of service to that ever-increasing body of citizens who wish to familiarize themselves with the general principles and the present status of knowledge regarding the animal kingdom.

In a subject that is undergoing rapid change and constant addition, it is impossible that a text-book should present the latest word on every topic. The effort here has been rather to show

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PREFACE the established facts and avoid in the main the unsettled or debatable problems, or to present them in such manner as to enable the student to understand and estimate the discussions on such questions in current literature.

While the writer is indebted to many sources for material worked into this volume, and while it is impossible to enumerate these in detail, it seems fair to mention in particular the publications of the Bureaus of Entomology, Animal Industry, Fisheries, and the Biological Survey of the United States Government, which have been most important sources of information. Many of the illustrations are reproduced here by the kind permission of the Officers of these Bureaus.

I have also been favored with drawings for reproduction from a number of my students, those by Miss Detmers and Messrs. Sim and Shira deserving special mention. My son has assisted me to several photographs.

I desire to acknowledge the kind assistance of Professors Herms, Hine, Jackson, and Walton, and of my wife, who have read certain chapters, and especially the helpful criticisms and suggestions of my associate, Professor F. L. Landacre, who has read the entire manuscript, has tested portions of it in his classroom, and given me the benefit of his rich experience as a teacher. I am also much indebted to Professor E. L. Rice for a critical reading of the proof, and to the publishers for their liberality in the provision of illustrations.

HERBERT OSBORN.

Ohio State University,

Table Of Contents

CHAPTER PAGE

I. Introduction i

Zoological Classification, I ; Animal Functions, 6.

Chapter I

Before taking up the detailed discussion of our subject, it may be in place to consider briefly the aims in view, and methods by which we undertake to secure a knowledge of our subject.

Zoology deals with the subject of animal life, and considered in the broad sense this must be interpreted as including whatever pertains to the life of the animal. We are not to consider merely the structure, or the classification, or the habit of animals, but, with all these phases of study, we are to consider the relation of the different forms of animals to each other, and also their relation to mankind, since these have in a great measure affected the course of development and determined the conditions of existence of the different kinds of animals. It is evident that but a small part of this subject can be covered in an elementary course, but it should also be remembered that whatever observations one has been able to make during his lifetime are to be considered a part of one’s available material to be systematically arranged and correlated with what may be learned of other forms or other phases of life in the animals studied in a definite course.

While we doubtless realize, if we stop to think a little, that animal life is a most abundant feature on the earth, it is perhaps hardly possible to conceive of the immense variety and extent of living organisms which have been, or are at present, distributed over the earth.

While there is a fundamental similarity between plants and animals, a close agreement in the basis of life activities, there is no question as to where we place the majority of the forms with which we are familiar.

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We never doubt as to the position of the horse and the grain on which it feeds or think of confusing the more characteristic structures or activities of such a form as a bird and the tree in which it may nest.

While, therefore, we should fully recognize the points of unity and remember that among some of the simplest it is difficult to distinguish plant from animal organisms, we need not be particularly concerned as to the questions involved in separating them.

Animal life in some form occupies practically every corner of the earth; occurring in the oceans, even at a great depth, and on land even in the most unfavorable conditions of dryness and of altitude, so that from the most favored conditions of warmth and moisture to the most unfavorable conditions of heat and cold some form of life will almost certainly be found. That animals existed in great abundance in the past, is clearly shown in the fossil forms that are found in different rock strata, running back as far as the oldest stratified rocks that are known. This branch forms a distinct field, called Paleontology.

While we know but little as to conditions in which life originated, we must assume that it arose primarily from inorganic matter, but so far as known at the present time, living forms arise only as descendants of parent forms, and we can only infer that this process has been continued from a very remote period. It is apparent, however, that in the lapse of time, animal life has changed and that while existing species must have descended from those occurring in the past, there has been some process of modification, so that the ancestral forms, if traced back far enough, would present different characters. Our present concern, of course, is more directly with forms of life existing at the present time, but it will be of interest to inquire how these forms are related to those forms which have preceded them and the evidences of which are preserved for us in fossils. The number of species living at present is doubtless as great, if not greater, than at any time in earlier history, and while many kinds have become extinct, their numbers have been more than made good by new forms that have been arising.

Classification. — The grouping of animals into divisions in which similar kinds are placed together or classified has two objects in view: first, as a matter of convenience to bring together those which are similar and to designate them by some common name, so that they may be referred to in general terms. The group of birds, for instance, under this general name carries with it an animal with feathers and wings that are characters common to all kinds of birds. The other purpose, and more fundamental one, is to indicate the natural affinity of kinds so associated, or in a deeper sense to associate those that have had common origin or ancestry. Birds, again, for example, although occurring in thousands of different kinds at present, may be assumed to have arisen from some generalized ancestral bird, unlike any occurring at present, but which possessed a covering of feathers, possibly had wings, and possessed other structures which are common to all birds.

We arrange all animals included under the animal kingdom into branches (phyla), divide these again into classes, and classes into orders, and orders into families, families into genera, and genera into species, the species being recognized as the unit in nature, or including individuals of such similar features as not to be easily separable, or so similar as to readily interbreed.

Closely related species are grouped into genera, so that a genus is simply an arbitrary assemblage of species. There may be any number from one to one hundred or more, and nearly related genera are again assembled in families, families into orders, orders into classes, classes into branches, which are finally combined in the animal kingdom as a whole. When we speak, therefore, of a general group, as birds, fishes, mollusks, etc., we should have in mind the fact that these general groups include an immense number of kinds of animals and that each is divided into orders, families, genera, and species according to one general plan. In common usage, the name of the animal stated in scientific terms consists of the genus and species name, the genus always being given first, as, for instance, Canis familiaris, the dog, while another species of the genus, the coyote, for example, would be Canis latrans.

While no one can expect to become familiar with the names of all these different kinds of animals or even minor divisions of them, the names of the principal groups, and such forms of animals as are dealt with more particularly, will gradually become familiar, and without any effort at memorizing one should come in time to recognize them just as he would the names of familiar friends. No attempt should be made to learn the name of a group or an animal unless it can be associated with a definite character or fact covering such a group or animal.

Aside from the relation of species, members of a common genus, or common family, we must stop to consider also the relation existing between the different species which occupy the same locality or which in their habits are in some way dependent upon each other. We know that certain animals depend for their food upon catching and devouring other animals and are in this way dependent upon them, while in other cases, as in parasitic forms, one animal serves as host for another and is preyed upon in such a manner that it may not suffer very great immediate loss, but in time or with an excessive number of parasitic forms may be weakened or even killed. We find that in thousands of ways these dependencies of one animal upon another enter into their actions and control their ability to thrive and multiply, and further, all animal life, in the end, is dependent upon the growth of plant life, since animals are incapable of transforming inorganic matter or substance directly into organic matter. Plant life, on the other hand, feeds in general upon inorganic matter and serves to change it to organic matter, so that in the last analysis we may say that all animal life is dependent upon plant life. The cycle of changes which may occur, however, between any particular animal and the plant life which serves it as food would be too intricate to follow, as it may feed upon some weaker form of animal, and this again upon other animal forms, in an extended series, until at last some forms are reached which are dependent upon plant life.

If we consider man as simply one species of animal, and that like other animals he is dependent upon other forms of life for subsistence, it is easy to understand that nearly every form of animal will possess some important interest to the human species, and that an exhaustive study of an animal may eventually result in important knowledge as to its relation to human life. Inasmuch as Economic Zoology is simply an application of our knowledge of animals which affect human interests, it is easy to see that almost any phase of the study will have some bearing on the problems that concern us. Economic zoology, if studied thoroughly, must of necessity be based on accurate knowledge regarding structure, relations, habits, and activities of animals, so that it involves a study of the whole animal and all that can be learned regarding its activities. Some of the facts which concern us most directly are regarding those animals which we use for food, such domesticated animals as cattle, swine, etc.; those which are taken for game, many kinds which are caught from seas or rivers, as fish, turtles, frogs, oysters, etc.; those which furnish clothing material, such as wool, furs, and silk ; those which are detrimental in attacks on our crops or upon our domesticated animals; or those which may attack us directly or which are annoying or injurious or which in some instances may be of some importance as carriers or transmitters of disease, as in malaria or yellow fever; or again, those which invade our dwellings and feed upon our stored foods, clothes, carpets, etc. ; those which are poisonous and whose stings or bites are both annoying and dangerous and those which act as scavengers, disposing of organic debris. Many of those which furnish food supplies or clothing material enter very largely into commerce, and we need only mention such terms as beef, milk, butter, fish, oysters, pearls, pearl buttons, ivory, hair, furs, sealskin, feathers, ostrich plumes, horn, tortoise shell, bone, honey, beeswax, sillf, lac, cochineal dye, etc., to suggest some of our greatest industries and most important articles of commerce.

Then again, a knowledge of animal life may be of great importance to us as illustrating certain fundamental biological principles which should be understood as being effective in human Society as among the lower groups of animals. Such general principles as are exhibited in parasitic animals and sedentary animals, or as may be learned in the complex relations among the gregarious and social species, may teach us most valuable lessons as to principles of human society or as to the consequences which must certainly follow the adoption of certain modes of life.

Animal Functions

There are certain activities which are common to all kinds of animals, and a recognition of which will help greatly in understanding the definite structure or organs which are concerned in the life of animals. All animals must obtain nutrition in one form or another, that is, all animals must have food, and this implies some method of taking in food material and that this be appropriated by the tissues of the organism. In its simplest condition, this may be simply inclusion of organic matter or substance which can be utilized by the protoplasmic content of cells. Usually, however, some distinct process or change takes place before nutrient material is available for special tissues. This may consist simply of digestion or the results of digestion being absorbed into or assimilated by cells that surround it, but in animals of larger size there must be some method of distribution, and this results in the systems of circulation and special forms of assimilation. Nutrition, as a general factor, may include, then, such processes as prehension, or the collecting of food; ingestion, or the swallowing of food; digestion, or the change to a soluble or assimilable condition for absorption; circulation, or distribution and assimilation. Connected with nutrition also, or following metabolism connected with tissue activity, is the resulting waste or nitrogenous products which must be eliminated from the tissues, and which processes are known in general as excretion. 1 hese are eliminated by some form of kidney.

Closely connected with nutrition also is respiration, which supplies one essential element (oxygen) in the activity of the animal, which combines with carbon in a process similar to combustion, thus giving rise to carbon dioxide. Another very general group of activities may be considered under the head of locomotion, All animals for part of their life or in some parts of the body have the ability to move, and this is based upon the property of contractility residing in the protoplasm or, for all the higher animals, in special tissues, as the muscle. Locomotion, however, is connected with a very great variety of structures, among which may be mentioned pseudopodia, cilia, flagella of protozoa; the parapodia and setae in worms; the swimmerets and legs in crustaceans; legs and wings in insects, and fins, legs, paddles, wings, etc., in vertebrates.

Another distinct series of activities is represented in the sensibility or sensation possessed by different animals, or simply a condition which may be represented by the irritability in the single cell, or a response to contact or stimuli of different kinds by contracting or changing form, or in movements of the cilia or other surface structures. In more specialized forms this is represented by more special senses, as touch, taste, smell, hearing, and sight, for which numerous complex organs of sense are developed, the most extreme of which are represented in the eyes and ears of animals, which are most perfectly endowed with sensitive organs. We have, then, three great groups of activities in nutrition, locomotion, and sensation which are essential to the life of the individual and which are found in some form in every kind of animal organism. It is essential, however, to the perpetuity of every kind of animal that it should be able to reproduce its kind, and this gives us a fourth general function — that of reproduction. This is presented in some form in all kinds of animals, but there are a number of different methods of reproduction and processes by which the number of individuals may be multiplied and hence the perpetuity of the species assured. The simplest form is that of division of an individual into two, and successive divisions of the resulting individuals. This is the most common method amongst the single-celled animals. Amongst the higher forms there is usually the development of two sexes or individuals producing germinal elements of a different character and the union of which is essential to the formation of a new individual. Special modes of reproduction will be noted in the different groups as they are considered.

The activities mentioned are those which concern the individual or the species, but if we consider the actual existence of the animal in life, we must recognize those activities which are related to other organisms or its surroundings. Every animal is dependent for its existence upon the presence of certain conditions of environment, including air, water, food, etc. Often a very complicated combination of conditions is established by forms which have succeeded in maintaining their existence, and a study of these relationships constitutes a most important phase of Zoology, ecology. This perhaps can be seen by an example, such as, for instance, the rabbit. This is a plant feeder, and by itself the main condition necessary for its existence is an abundance of plant food. The rabbit, however, multiplies with great rapidity — a single pair being able to produce within a year probably as many as several hundred of progeny. It would be but a matter of a short time, if their increase were unchecked, until all available food in any given locality would be exhausted. In their native conditions, however, rabbits are fed upon by foxes, wolves, weasels, skunks and other carnivorous animals which serve to keep their numbers reduced. Taking one of these carnivorous forms, we can see that successful existence for the fox would lie in the supply of rabbits as food material, but the increase of foxes would be largely limited by the supply of rabbit food, and if only these two forms existed, we would expect a balance to be established. Again, however, another factor is introduced, as the wolf, and there would be a contest between the two forms, both tending to further reduce the stock of rabbits, and the basis of supply for each of these species would result in the further limitation of the numbers or the driving out of the surplus individuals of one or the other species. This would be complicated still further, of course, by the inclusion of other forms, like weasels, skunks, etc., but, on the other hand, is complicated further by the fact that these forms are not dependent upon rabbits only, but that other carnivorous or herbivorous animals may be used as food, so that birds, chickens, squirrels, mice, and a considerable variety of species would be included in the combination. It is easily apparent that a full knowledge of all the factors which may enter into the life of one kind of animal is extremely difficult to secure, but that without some conception of these relations our knowledge of animal life would be very incomplete; that is, our knowledge of structure, or morphology, and activities, or physiology, must be supplemented by the knowledge of relationships to other organisms, or ecology, if we would properly appreciate the problems for any kind of animal.

The relations of this kind pass directly into relations affecting the human species, and with even this same example we can see that the kind of animals presented becomes of importance for the use of our own interests. Rabbits, for example, may be used for human food, or, on the other hand, in their attacks on our apple trees, shrubbery, etc., may cause us extensive damage, so that it is to our interest that predatory forms should feed upon them to such an extent as to reduce their number as much as possible; but these predatory forms may affect us by catching chickens or domestic animals which are of value to us, so that the relation for a given animal may have different aspects to mankind; that is, its economic status may vary in different localities or at different times, or from day to day, according to the character of food it may eat. With this very general outline of our subject and the purpose in view in our study, we may take up a consideration of the different animals in a systematic order, including in the different groups such discussion of a general nature as may be strikingly illustrated in particular groups.

Chapter II

The Protozoa are the simplest forms of animals and are very distinctly set off from the other groups by the fact that they are composed of but a single cell. This might appear to give them much greater simplicity than would be found in any other kind of animal, but some of them show very considerable complexity of structure, and perhaps, if various organs be considered, are really more complicated than some of the simplest of many-celled animals. There is, however, a fundamental difference associated with the single-celled condition that is most strikingly shown in the development. Since they are composed of single cells, it follows that there is no formation of germ layers in their development, but that whenever a division of cells occurs, the result is the formation of distinct individuals or at the most of colonies or aggregations of cells, each one being practically independent. While all are essentially microscopic, a few are large enough to be visible without magnification, but none of them can be studied without the assistance of a microscope.

They possess the essential part of a typical cell; that is, they consist of a minute mass of protoplasm which includes the nucleus and may possess a more or less definite wall. Along with these they bear locomotory structures of one kind or another, and some form of locomotion is present in practically all forms. Exceptions occur, for a large part of the lifetime, in some of the parasitic species.

One of the most common of the representative forms is the Amoeba, a minute, extremely simple form, that occurs in almost any body of quiet water, and will be found most readily upon

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submerged leaves or in the ooze adhering to sticks or other submerged objects. Seen under the microscope, this appears as a very minute particle of motile substance, usually moving with a peculiar flowing motion, the extension occurring in the form of irregular projections called pseudopodia. These mav be protruded or withdrawn, or in some cases the whole animal will

Fig. i. — Amoeba proteus, X 330. 1, nucleus; 2, contractile vacuole ; 3, pseudopodia; outer clear portion, ectosarc, inner granular, endosarc; 4. food vacuoles; 5, grains of sand. (After Gruber, from Shipley and McBride.)

appear to flow into one of these extensions. Often this results in a steady movement or translation, so that the animal will progress slowly across the field of vision. Examined closely, it will be found to consist of two rather distinct portions, an outer clear or more transparent part, the ectosarc, and a central, more granular and somewhat liquid portion, the endosarc. The latter may often be seen flowing in somewhat definite currents within the limit of the ectosarc. Within it will be seen also some larger granules of food material inclosed in food vacuoles, sometimes including such distinct organisms as diatoms or desmids. There will also be noticed a distinct, usually more brilliant part, the nucleus, which is the essential structure in the division of the cell. Contractile vacuoles will be seen from time to time and form gradually as clear pinkish globules within the cytoplasm, and then suddenly disappear by a rapid contraction. The contents of the vacuole are usually ejected from the cell. We have already noticed the manner of locomotion, and it will usually be possible to see also the method of feeding. This is very simple, the Amoeba merely flowing around the objects which it uses as food, and which thus become inclosed in the cytoplasm and their nutritive contents digested and absorbed into the protoplasm of the cell. The indigestible portions are then slowly ejected from the cell surface. There is no circulation except the movement of the protoplasm, and respiration consists in the absorption of oxygen from the surrounding water and the elimination of carbon dioxide.

It is believed that the contractile vacuole represents the system of excretion, the waste products of the activity of the protoplasm being collected in the contractile vacuole and from this ejected to the surface.

The mode of multiplication in Amoeba is extremely simple, but involves, doubtless, a complex set of changes in the nucleus. Before division there is a distinct separation of the nuclear parts and the formation of two distinct nuclei which separate from each other, and following this, by gradual constriction of the cell walls, the mass of protoplasm is completely divided, each part including one of the new nuclei. Each of the resulting Amoebae may later divide in a similar manner, and this process of division may go on indefinitely, resulting in the production of a number of individuals. Under certain conditions, however, the cell will contract into a globular form, the outer wall becoming hard and inactive, and the whole cell assume a resting, encysted, condition in which it will stand a great amount of drying and cold, and some degree of heat. It will regain its activity at any time with suitable conditions of moisture and temperature. It will be seen, then, that the Amoeba possesses locomotion, nutrition, the power of reproduction, and since it responds by contraction to stimulation, it shows also the function of irritability.

The Protozoa illustrate the fundamental activities of animal life and may serve as examples of the principles of animal behavior. Movement, which is characteristic of all animals and primarily due to contractility of protoplasm, may be stimulated by various external forces, and possibly by certain internal factors. So far as external forces are concerned there is opportunity for experimentation, and considerable progress has been made in determining the nature of these external stimuli and the responses that are made to them. These responses, or tropisms, have been classified with reference to character of stimuli, as for light, phototropism or phototaxis, and an organism attracted by light is said to be positively phototropic, or if repelled, negatively phototropic. The response to gravity is geotropism; to chemical stimuli (as in taste or smell), chemotropism ; to electricity or magnetism, electrotropism; to contact, thigmotropism ; to moisture, hydrotropism; to wind, anemotropism ; to heat, thermotropism; to current (of air or water), rheotropism; to food, trophotropism, etc. It may be noted also that the same organism may at one time be positive and at another negative to the same stimulus or may respond in a different manner to different intensities of the same stimulus.

It must be admitted that in addition to the movements that seem to rest solely on external stimuli and which can therefore be studied by direct experiment, there are other movements, especially those associated with reproductive processes, growth, metamorphosis, etc., that are not to be explained in such a simple manner, but are in effect due to certain internal and perhaps self-regulated forces that cannot be tested by the same methods. Of these we are largely ignorant, though it is not to be granted that they cannot be studied or explained by experimental methods; such activities become more complex and difficult with the greater complexity of organisms. The simple single-celled organism may respond directly to the application of a local single stimulus, while

Fig. 2. — Division (budding) of Euglypha alveolata Duj. The nucleus is shown in different stages of mitosis. The shell plates occurring in this species are stored in the endoplasm around the nucleus and stream out with part of the protoplasm to form daughter cells before nucleus is entirely divided. (After Schewiakoff, from Calkins’ Protozoa.)