THE

DE ANOPLURIS

By Professor G. F. FERRIS

STANFORD UNIVERSITY

HE distinguished professor had attained some portion of his distinction by reason of years of work spent upon a small and little studied group of insects. His wife and small daughter chanced into his laboratory one day and discovered a student examining one of these insects through a microscope. The small daughter demanded a look and then came the inevitable question, "What is that?"

"That," said the unsophisticated student, "is a louse.'

There was a moment of pained silence and then came the gentle but unmistakable rebuke from the professor's wife, "We always call them Anoplura."

Now these very insects are the subject of my present discourse and lest I again offend the delicate sensibilities of any one I have disguised my intentions by a title to which not even the most fastidious should be able to take exception. To be sure it means the same thing as something else that might have been used, but after all there is something in the name by which a thing is called. Even the scratching soldier, from whom one would least expect any delicacy in such matters, conceals the identity of these insects under the euphemistic titles of "seam squirrels" and "cooties." That the deference thus accorded them reduces in the slightest degree the frequency or the painfulness of their attentions may be doubted, but at least the victim is enabled thereby to retain a bit more of the shreds of his self-respect.

In fact under the name of "cooties" these insects may qurte properly become a subject even of parlor conversation. The word carries a faintly humorous connotation. One may without risk of immediate social ostracism speak of the great wads of hair that girls wear over their ears as "cootie coops.' True, such an expression might not be looked upon with favor in the most refined circles, but we need only reflect upon what would happen were the wording changed a bit to see what a concession has been gained for it to be used at all.

It is perhaps a fortunate thing that this has happened, for even entomologists, who should have put all squeamishness behind them, have been more or less reticent in speaking of these particular

insects. The remark of an author writing in 1842 that "in the progress of this work, however, the author has had to contend with repeated rebukes from his fellows for entering upon the illustration of a tribe of insects whose very name was sufficient to create feelings of disgust" might almost be justified to-day. In fact, in a rather recent entomological book it is said that "from their habits lice are not popular insects even for entomologists to take up," and certainly the amount of attention they have received has never been large.

Yet I confess to being a student of these insects and I do so without hesitation and without apologies. Not to me are they merely "disgusting parasites." Not to me is the term "louse man," with which my botanical and chemical and even entomological acquaintances, with a misguided sense of humor, see fit to address me, a term of reproach. For, know you, there are very few who can merit it, scarcely more than half a dozen men in all the world in fact. To us it is a title of distinction, an evidence that we few have been able to avoid the well-beaten paths of the butterfly and beetle hunters and strike out into a but little explored country. For us it is a country of much interest and-dare I say it?-even of some beauty. And it is my hope that in these pages I may lead others to see in these disgusting parasites, these cooties, some of the things that we, their devotees, are able to see.

For a proper understanding of these parasites, these lice, as I shall not hesitate henceforth to call them, it should be explained that there are really two quite different sorts of them. One sort, known as the bird lice or the biting lice, is found chiefly on birds, although there are a few species on mammals, while all the species of the other sort, the sucking lice, occur on mammals. There is a very great difference in the manner by which the species of these two groups obtain their food. The biting lice feed by biting off and chewing up bits of hair or feathers or skin scales while the sucking lice feed by inserting their beaks through the skin and sucking up the blood of their host. Such a difference in habit is a very important thing, for with it is most intimately bound up the matter of the potentialities of the insects for harm to the animal upon which they live.

It is now a firmly established and generally recognized fact that many of the most important diseases of man and of other animals as well are transmitted by insects. In by far the majority of cases the insects concerned are forms that live upon blood, that actually pierce the skin of the animal upon which they feed. Thus in feeding upon successive individuals these insects may transfer diseaseproducing organisms from one individual to another. This poten

tiality for evil is inherent in every blood-sucking form, and its possibilities are realized to a high degree in those blood-sucking lice that live upon man, the familiar "cooties" of the war period.

Under the conditions that usually prevail in armies it is impossible for soldiers to keep themselves free from these insects. Thus it was that certain diseases which are transmitted by the lice became especially prevalent during the late war. Typhus and trench fever are transmitted by lice, and as far as known only by lice, and the measures for the control of these diseases were directed chiefly against their insect carriers. The tremendous losses due to these diseases undoubtedly had a profound effect upon the fighting strength of the various armies. Who can say to what extent the course of the war may have been influenced by them?

There are a few other diseases of man that are known to be carried by lice, and they have been suspected of carrying several others. It is known also that an epidemic disease of certain small Asiatic rodents is transmitted by the sucking louse that occurs upon these animals, and it is highly probable that there are many other cases of the same sort.

On the other hand the biting lice, although far exceeding the sucking lice in numbers of species, are not known to be the carriers of any diseases. If they are abundant upon their host they may cause injury merely by the irritation of their crawling about or by the matting of the hairs or feathers to which their eggs are glued. Otherwise they are of no concern to their hest.

But however important and interesting this connection of lice with the transmission of disease may be it is not the only thing about them that is worthy of consideration. This connection with disease is simply a fact, and after all faets are not always as interesting as theories, even though they may be more important. Any one should be able to travel the plain and open road of fact, but there is more pleasure in the narrow and devious trail of theory that occasionally takes the traveler up into the high places-and threatens always to lead him into a bog from which the utmost of mental agility may not be sufficient to extricate him! The most interesting thing about lice is not these highly important facts of hygiene. It is that they may be made to yield a contribution to biological theory.

The starting point of this contribution is the fact that by far the majority of all the different species of lice, both of the biting and sucking groups, are found upon a single species of animal or at the most upon a few very closely related species. It is a curious fact that although horses and cattle and sheep have for many hundreds of years been in close contact in their stables each has re

tained its particular kinds of lice. There are at least four species of lice upon domestic cattle, but these do not occur upon horses or sheep. There are at least three kinds upon sheep, but none of these has been taken from horses or cattle. There are at least two kinds on horses, but neither of these has been taken from cattle or sheep.

These instances may be paralleled by many others. The inference is obvious. It is evident that under normal conditions each species of louse "prefers" to feed upon a particular kind of animal. In other words it is adapted to feed upon the blood or epidermal structures of this particular host and does not find the blood or the epidermal structures of another kind of host a suitable food. Furthermore these insects are very reluctant to leave their host and even after its death may be found clinging to the hairs or feathers. Under experimental conditions lice have been fed upon animals very different from those upon which they normally live, and it is true that sometimes under natural conditions they may be found upon an animal on which they do not belong. Still this does not change the fact that usually each species of louse sticks pretty closely to a certain kind of animal, passing from one individual to another in the nest or at mating time. Thus it is that the parasites are in a way inherited by the young from their parents-heirlooms, if I may be pardoned an atrocious pun.

The next fact of interest is that the same species of louse may be found upon distinct but closely related species of birds or mammals in widely separated parts of the world. Thus we have upon the kingfisher in North America a louse that is the same as one on a kingfisher in Egypt. Another species is found upon various species of hawks throughout the world. Another is found on seals in both the Pacific and Atlantic Oceans. Another is found on ground squirrels in Siberia and in North America.

Now all these animals are so widely separated that certainly it is impossible for the louse of the African kingfisher to transfer directly to the North American kingfisher or for the louse of the Atlantic seal to transfer directly to the Pacific seal or for a transfer to take place in any one of the many other cases of this sort that might be mentioned. Then how has the parasite managed to get upon both of its widely separated hosts?

There are enough facts of this character to demand some attempt at a logical explanation. There must be a reason for them. If we remember that these parasites are normally passed down from one generation to another as a sort of racial inheritance and if we follow far enough the train of reasoning that is thus initiated we can not but conclude that at some time this African kingfisher

and the North American kingfisher, or the North American ground squirrel and the Siberian ground squirrel, or the members of any such pairs as we may name, were together as a single species. We have a set of facts that can not reasonably be explained unless we accept the theory of evolution. The conclusion is inevitable that at some time these kingfishers, or whatever they may be, had a common ancestor and that the shifting of land masses or climates or some other cause has left part of the descendants in one corner of the world and some in another and that there by various evolutionary processes they have become sufficiently different to be recognizable as different species.

One of the most remarkable examples of the working out of such a change is that of the llama and the camel. The paleontologists tell us that at one time there were many more species of camels and camel-like animals than there are now and that these animals first appeared in the New World. At the present time, however, the only remaining representatives of this group are the llamas of South America and the camels of Asia and Africa. Yet, separated by half the world-these cousins, or forty-second cousins, still show their relationship and their common ancestry not only in their bodily structure but in their parasites as well, for on both there is found the same species of louse.

We can extend the list of facts much farther and still the answer of common ancestry is the only reasonable explanation of them. The louse of the domestic hog has its nearest relative in the bush pigs of Africa. The lice of one kind of squirrel are more closely related to those of other squirrels than they are to the lice of other animals. The lice of the domestic chicken have their nearest relatives in the many different species of lice upon the other chickenlike birds.

Like nearly all theories, however, this one must allow for certain exceptions. We can lay down a general rule but it is almost too much to expect it to work always, at least if we are dealing with such things as living organisms. It is one of the difficulties in the way of the study of living things that they refuse to stay put. They simply will not go always into the little pigeon holes that we block out for them. Like men they must at times assert their individuality by breaking our trifling little laws; they at times demand the right of living their own lives in their own way. In some instances related species of lice are found upon animals that are certainly not very closely related and sometimes different species of lice are found on animals that really ought to have the same kind. So it must simply be admitted that in some cases other influences have been at work. Still the broad facts remain as I have pictured them.