might develop from unfertilized eggs. According to Onions, the workers of a South African race of honey-bees are able to produce workers parthenogenetically, and Reichenbach, Mrs. A. B. Comstock and Crawley find the same to be true of worker ants of the genus Lasius.

I believe that Phillips, in the remarks above quoted, suggests an important fact which has been too little noticed and may account for much misunderstanding in regard to sex determination in the honey-bee. Accurate knowledge of the life-history of a particular individual in a colony of social insects is almost or quite unattainable, for two reasons: first, the egg can not be isolated and the larva brought up by hand, like a young chick, because it requires the presence of nurses of its own species and they will not rear it under abnormal conditions; and second, the workers of many social insects are very fond of eating the eggs and young larvæ and these same workers or the queen not infrequently at once lay eggs in the place of those devoured. This behavior is especially common and disconcerting among the ants. Now a rigid control would require not only that the mother insect should be observed during the very act of oviposition but that the egg and resulting larva should be kept under constant observation day and night till the completion of development. A relay of observers, changing every few hours for two or three weeks, would therefore be needed in order to make sure that a particular adult had developed from a particular egg, and it would be necessary to observe many individuals in such a manner before we should have the data for accurate conclusions. In fact, we shall need all the resources of a specially equipped laboratory, with a specially trained staff, for aný final solution of many of the peculiar developmental problems suggested by the honey-bee and other social insects.

Among these problems we should also have to include that of the differentiation of the two female castes, that is, the problem as to whether the worker and queen arise from one kind or from two different kinds of eggs. The experiments of transferring larvæ of different ages from worker to queen cells, as previously stated, and the existence of series of transitional forms between the worker and the queen, naturally lead to the view that there is only one kind of female egg and that the character of the larval food after the fourth day determines whether the adult is to be a worker or a queen. This may be true of the honey-bee, but, as we shall see, observations on certain ants and termites indicate that there may be more than one kind of female egg.

The main object of the rich and abundant food administered to the larva of the queen honey-bee is evidently the rapid develop

ment of her ovaries, so that she may begin to lay eggs very soon after emergence. This is also indicated by the conditions in the Meliponinæ. The Melipona queen, which is reared in a closed cell of the same size as that of the workers and on the same amount of food, emerges with rudimentary ovaries and has to develop them by subsequent feeding during her adult instar, whereas the Trigona queen, which is reared in a large cell with more food than is given to the worker larvæ, emerges with mature or nearly mature eggs in her ovaries. All these queens, however, are distinguished from the cospecific workers by certain degenerate or primitive characters, which, it would seem, must owe their peculiarities either to the indirect, inhibiting or modifying action of chemical substances (enzymes) in their food or to the more direct action of hormones, or internal secretions produced by the developing ovaries. The great size of the ovaries in the queens of all these social bees accounts, of course, for their extraordinary fecundity and the size of their colonies. Cheshire computed the number of eggs which may be laid during her lifetime by a vigorous, fecundated honey-bee queen as about 1,500,000, and, according to von Buttel-Reepen, we should find in her spermatheca no less than 200,000,000 spermatozoa. It is not surprisisng, therefore, that a hive, at the time of its climax development during the early summer, may contain 50,000 to 60,000 or even 70,000 to 80,000 bees.

In conclusion I may refer to one of the negative peculiarities of social bees-the absence of that peculiar interchange of nutriment between the adult and larva, or trophalaxis, which seems to be a powerful factor in integrating and maintaining the colonies. of the social wasps. Among the Meliponine the food and egg are simply sealed up in the cell, so that there can be no contact between adults and larva, and even the honey-bee worker does not place the food on the mouth of the larva but pours it on the bottom of the cell where it can be imbibed when needed. So far as known, the bee larva, unlike the wasp larva, produces no salivary secretion to attract its nurses, though it might be going too far at the present time to say that this is certainly not the case. It is quite probable, nevertheless, that the sources of the development and perpetuation of adult and larval contact, so essential to the maintenance of social life among the Bombinæ, Meliponine and Apinæ, are to be looked for in other directions. Hermann Müller long ago pointed out, as I stated in the preceding lecture, that the transition of the adult wasp from an insect to a nectar and pollen diet was due to economy of food. These latter substances represent a very concentrated and energizing food supply and one that can be

more readily obtained in great abundance than insect food. Hence it is not surprising that a large group of insects like the bees has become so exquisitely anthophilous, and that the exploiting of larval secretions is unnecessary. It will be noticed that all three subfamilies of social bees store quantities of pollen and honey in open cells and such easily accessible stores of liquid and very finely divided food make even the reciprocal feeding of the adult workers in bee colonies superfluous. This storage of food may be at least one of the reasons why such exchanges of nutriment as we observed among the social wasps and shall see again in a more exaggerated form among the ants and termites were either never developed or were long ago discontinued by the social bees.

Vol. XV.-22.

THE PATH AS A FACTOR IN HUMAN
EVOLUTION

THE

By RALPH E. DANFORTH

UNIVERSITY OF PORTO RICO

HE path and the wilderness, formerly in harmony, are now at odds. Certain elements of the wilderness are essential to the best evolution of man. The path is also essential; therefore a reasonable measure of harmony between it and the wilderness should be restored and retained. This restoration and retention might be included in our broad term conservation.

Millions of years before man became human some of the primitive worms and insects made paths; some of the lower vertebrates did likewise, and many of the earliest mammals of remote Triassic times doubtless made paths and runways of many sorts. The Triassic, Jurassic and Cretaceous together constitute the Mesozoic, or age of reptiles, which according to some geologists lasted nine million years; and throughout this long time our earliest mammalian ancestors were small creatures, the largest not exceeding a rat or rabbit in size, hiding for their lives from many a reptilian foe, both large and small.

With the close of the age of reptiles and dawn of the age of mammals, which some estimate to have been three million years ago, mammalian species evolved with great rapidity and in many directions. Mammals small, medium and large, and of wonderful diversity were produced. Of these some still made paths of one sort or another, and many of their constantly evolving offspring continued to do likewise.

Among our modern mammals we now find many famous pathmakers. When man's more recent ancestors departed from arboreal life and remained more upon the ground again, like their remoter pre-arboreal ancestors, they must have made frequent use of the ready-made paths of their contemporaries, some of which fell victims to early man, while others at times made of him a victim. From that time, throughout the many thousands of years of savagery man made an increasing use of paths, himself becoming an important pathmaker where he walked from place to place repeatedly, yet often departing from his paths to search the all-surrounding wilderness.

Some of the ablest students of human evolution to-day assert that earliest man lived in a part of Asia where the physiography and climate were changing so that the abundant rain-forests were gradually forced to give place to a dryer and more open park-like country; changes which obliged the arboreal inhabitants either to migrate or to perish or to modify their mode of life. Potent as such environmental changes may have been as aids to man's transformation from an arboreal creature to a terrestrial man, there were doubtless other deeper-seated factors contributing to the same end. This change from an arboreal to a terrestrial life has been a fruitful field for thought research and discussion among men of science, and it is likely that more thoroughgoing investigation may throw more light upon it. But this is a digression from my theme. Whatever the causes, the fact of the change is plain, and not doubted by any biologist.

Throughout the long, ensuing age of human savagery man had his paths, yet breathed the same pure, dust-free air to which the lungs of his mammalian relatives and ancestors had been accustomed. The lungs of his reptilian and amphibian relatives and ancestors breathed air equally pure.

The age of savagery gave place to the age of barbarism. Some of man's paths became crude streets and highways. Domestic animals, small or large, strayed or were driven along the ways. The wilderness became more netted with paths, and portions of it here and there gave place to crude agriculture. But it still was essentially the same wild, beautiful, fascinating thing. Wonder and mystery, game, adventure, peril, excitement and peace were found in the wilderness. The forests and the mountains, the lakes, valleys and streams ever lured the early children of men to wander into the wilderness, seek out its treasures, and learn its secrets by a life of daily familiarity. Some, less bold, dreaded the wilderness. Some, precocious in urbane awakenings, kept to the beaten paths. Some, indolent or effeminate, stayed to be pampered or scolded by the women. None of them remained within cave or within hut very long, for daylight was preferable to darkness or flickering firelight when storm or sleep did not drive them in. Window glass was not to come until long after civilization had replaced barbarism. Any opening in a dwelling admitted not only light, but volumes of outdoor air. Woman's work must be done out in front of the primitive dwelling place for light. The indoor life could not be lived by any one. Such were our forerunners for countless generations. Our artificialities of the present day are of mushroom growth, having sprung up, as it were, in a moment in contrast to the long ages we have been living the more natural, outdoor life. Our muscles were built for daily exertion, prolonged and varied,