readily be caught during the first week or two. At this age the bill is about two inches long, comparatively stout throughout, and scarcely decurved.

Among the smaller birds of the boundless prairie, a few species are specially notable. The commonest and most universally dif fused is the western horned lark (Eremophila alpestris leucolama); we find it breeding everywhere. It begins to lay very early; the curiously speckled young ones, quite unlike the adults, may be taken any time in June, already flying; while eggs (doubtless of a second brood) may be secured through July. The mode of nesting of the larks, and of the three most conspicuous prairie fringillaries, is substantially the same. The three to which I refer are the bay-winged bunting (Pooecetes gramineus confinis), the chestnut-collared bunting (Plectrophanes ornatus) and Maccown's bunting (P. Maccownii). These two Plectrophanes are the most characteristic of the prairie sparrows, and are found together in abundance in most of the regions here under consideration. P. ornatus however, is rather the more easterly of the two. Thus, it is common all over northern Dakota and the eastern part of Montana; while I have seen none since I came the first few miles up the Milk river, where P. Maccownii increases in numbers, then becomes the prevailing, and finally the only species. The chestnutcollared has a very pretty habit of soaring, like Sprague's lark, while the female is incubating, singing in the air, and letting itself gradually down like a parachute, with the wings stretched upward at a right angle with each other- an action that displays the glossy black of the under parts and the white of the tail to the best advantage. Floating thus lightly in the air they remind one of butterflies; and their song, though not of the highest excellence, is sweet, gladsome and musical.

Great numbers of water-fowl stay their flight to nest in the pools and sloughs of our Northern Boundary; among them may be mentioned mallards, widgeons, shovellers, teals, pintails, scaups, buffle-heads and wild geese. To resume the subject with which this slight article began, namely, exceptional modes of nesting, I would say that the geese of this region sometimes nest on the ground around the ponds, as geese ordinarily do, and then again. they sometimes nest in trees, somewhat like wood ducks, only that they do not enter holes for this purpose. Arboreal nidification of geese sounds strangely, but it is nevertheless true; and it is a well

known circumstance to those persons who inhabit the country, however unenlightened ornithologists may be in the matter. It furnishes a case parallel with that related by Audubon, of the herring gull nesting in communities, in trees.

I will conclude with an observation on the digestive arrangements of the sage cock-a bird which I have only lately seen alive. It has been repeatedly stated to feed exclusively upon sage leaves. All those I shot had the craw full of grasshoppers and other insects, and had nothing else in it. It has also been asserted that the bird has no gizzard; the gizzard is indeed quite thin, so as to appear merely a membranous bag, but for all I could see that the disposition of the muscles is the same as that obtaining in other gallinaceous birds. The case is simply a reduction of the amount of muscle, without any essential change in arrangement. At least this is the result of an off-hand dissection, such as one would be likely to make in the field. The change is an evident adaptation to the soft and succulent or juicy nature of the bird's food-buds, leaves and insects, instead of grain. There is another peculiarity of this bird, also dependent upon its food, and the nature of the digestive process. When flushed it almost invariably acts in the way which has given the green heron (Ardea virescens) its inelegant popular appellation.— Milk River, at 49°, July 25, 1874.

THE METAMORPHOSIS OF FLIES.* I.

BY DR. AUGUST WEISSMAN.

BEFORE I pass to the general results of the foregoing observations a short chronological exhibit of all the processes of development will be useful.

In agreement with all the earlier observations on the embryology of other insects it is apparent that during the life of the larva, in its outer form as well as the internal organs, only the

*Though Weissman's famous work, "The Development of Diptera," was published as long ago as 1864, yet we feel sure our readers will value the translation of a few of the concluding chapters which have not previously been rendered into English. The present chapter is entitled "View of the Phenomena of Development.”—A. S. P.

phenomena of growth are manifested, and not a deeper reaching metamorphosis. As the enlargement of an organ by simple growth in the Vertebrates is allied with a new formation of blood vessels, so here the origin of a new trachea is accompanied by the speedy enlargement of muscles and intestine, and with this very impor tant continual increase of the net-work of trachea is combined an expansion and increase in volume, so that after the first moulting, on the anterior end of the body, a new pair of stigmata are formed, while the aperture in the hinder one is doubled, and after a second moulting, a three-fold aperture is made.. Accompanying this is a certain change in the apparatus of hooks arming the mouth of the larva. All these changes are not of great importance; they lead to no new feature in the organization of the animal; they are series of processes which precede the formation of entirely new organs or parts. Transformation in this last sense occurs only in those parts of the larva, out of which the parts of the adult insects are developed. The genital glands, as well as the outer skin of the segments bearing the appendages of the fly's body, are already formed in the larva; indeed they are even formed during the development of the embryo.

*

We find ourselves in fact almost going back to the encasement theory of Swammerdam, who believed that the larva, pupa and butterfly were imprisoned from the very first in each other, and came to light by the successive casting off of each skin. It is in fact only this, that the parts of the fly do not all lie perfectly formed within the larva, but exist only as rudiments, and that only a part of the body of the fly is newly formed, while some of the parts will be produced out of the larva. The head and thorax with their appendages are formed within the larva by the gradual development of special cell masses. The abdomen, however, arises through a simple change of a number of larval segments. The head and thorax arise not as a whole out of a single cell mass, but in separate pieces, out of which after pupation the whole form is perfected.

The head arises out of two groups of cells which originate from a nervous filament sent off from the supra-oesophageal ganglion; but each segment of the thorax arises out of four separate groups of cells which are partly inserted in the course of a slender filament, and are in part blended with the peritoneal skin of a trachea.

*This chapter relates wholly to Musca vomitoria.

These collections of cells form flat disk-like bodies which are enclosed in a structureless membrane and may be termed the imaginal disks. In each imaginal disk of the thorax arises a quarter of a segment with the appendage belonging to it; the two imag inal disks of the head, the appendages of the brain, unite themselves into a hinder division, the eye-disks; and an anterior which forms the germ of the antennæ and remaining portion of the head.

The pupation in Sarcophaga occurs eight or ten days after the exclusion of the larva from the egg. It is accompanied by a marked contraction of the whole body, with an infolding of the first segments.

Under the hardened, barrel-shaped, larva skin [puparium], the true pupa is formed, i. e., the body of the fly enclosed by a special membrane, the pupa-sheath. The process of formation of the body of the fly, while thus enclosed, lasts for four days after the pupation. Then it reaches that stage which in the development of the butterfly is shown by a stripping off of the larva skin, and the formation of the pupa is ended; then begins the development of the same. This consists in the building up of the external form of the body, and in establishing the position and development of the internal organs. This period can be divided into two sections, which are here described chronologically. The first division consists of the more delicate modelling of the outer form. Hitherto the insect has appeared only in its crudest shape, the appendages of the thorax and head are but rudimentary, neither attaining their full size, nor their definitive form. All these parts are now entirely formed, and are matured in from two to seven days, and already covered with colorless hairs and bristles.

The second division covers the period of the eighth to the twentieth day, during which time the inner organs are completed, and the outer surface of the body assumes its peculiar colors.

The first period, that of the formation of the pupa, lasting from one to four days, begins with the destruction of the four anterior segments of the larva. The hypodermis which gives it its form is loosened, the muscles of the body-walls, as also of the pharynx, the cellular walls of the pharynx itself, the anterior part of the œsophagus, with the sucking stomach, follow next. During this time the thoracic pieces are developed from the imaginal disks; they give origin to the appendages, which are indeed very short, but still each joint can be distinguished, and are nothing but a

projection outwards of these same thoracic pieces. However here as we had until now thought-the appendages of the imago do not result from a simple thrusting out of the larval hypodermis, as would seem to be correct in a morphological view, which would consider the appendages of the insectean body as projections of the skin, during their development not aborted, but persistent. They are in fact still, however, projections outwards of the skin, though they are formed at a time when the skin has not grown into closed segments. Still we find at the end of the second day the formative disks of the thorax appended to their pedicels (nerves, trachea) in the form of swollen transparent vesicles, and within them the thoracic pieces to which they are closely related, with its appendage, can be easily observed. In three days they have attained their perfection, the skin peels off and falls away, and they now become three completed rings, the thoracic segments. At the same time the trachea of the larva are thrown off, and then begins the formation of a peculiar tracheary system, which performs its functions only during the pupal period. In its trunks and larger branches it resembles the larval system, but in the terminal rings is unlike anything else. In this respect their structure is very peculiar, in that all the ends project freely into the liquids of the body, and nowhere, as before, do they send fine branches to the different organs. The filling of the new system of air vessels with air does not go on during the remaining moultings, through a removal of the old proximal tubes (intimaröhren); this cannot be completely seen during the life of the pupa, but through the cross division of the proximal tubes (intimaröhren) in a determined place of the stem near the anterior stigmata.

At the third day the three segments of the thorax unite to form a small ring which posteriorly coalesces with the edge of the fifth larval segment; but the anterior edges are puffed up and are open. In the opening lie loose the chitinous parts of the mouth parts, the apparatus of hooks. The head of the fly is not yet to be seen, but the rudiments of the same are still visible within the thorax. In the two formative disks of the body, which we would consider as appendages to the brain, develop into a vesicle containing the œsophagal ganglion, the head-vesicle, on which the eyes and antennæ are already indicated, and from under whose hinder edge the proboscis grows out. On the fourth day the head, which has advanced forwards from within the thorax, comes to light, and is