scope, we see that the central stem carries on each side a row of barbs, which interlock with each other. The magnifying power shows us that these barbs are not simple filaments, but are themselves doubly bearded in the same fashion ; and further, that these little beards, called barbules, of the second series, are furnished with a third series. It is in this third series of filaments, called barbulets, that the tenacity in question resides. If we isolate one of the primary beards, by stripping away a few on each side of it, and again put it on the stage, we see that the secondary barbules of one side are armed differently from those of the other side. Those of the lower side carry short and simple barbulets, whereas those of the side which looks towards the point of the feather bear much longer ones ; and, moreover, many of them are abruptly hooked backwards. Xow, whenever the primary beards are brought into contact, some of these hooks catch on the barbule next above, and, slipping into the angles formed by the barbulets, hold there, and thus the two contiguous beards are firmly locked together. In the beard of the goose-quill, the structure is essentially the same, but the barbulets are far more numerous and more closely set ; they are also proportionally much larger—both those which are hooked and those which are simple. Indeed, the latter manifest a tendency to the hooked form, and by all these peculiarities the interlocking power is augmented. It is interesting to observe the great expansion of the beard in a direction towards the interior surface of the feather—

barb fbom GoosB-QiiLL. towards the stroke, as I just now

observed. This is to increase the resisting power, as a thin board set edgewise will bear a great weight without bending or breaking, provided it can be kept from yielding sidewise. The barbules are arranged only on the very edge, the upper edge, of the beard.

We will now examine some specimens of scales of Fishes, all of which are very interesting and beautiful objects, under low powers of the microscope ; though higher powers are requisite to resolve their structure. We will use both.

The scales of almost all the Fishes with which we are familiar, fall under two kinds, which have been named -ctenoid (or comb-like), and cycloid (or roundish). The

SCALES OF PEBLH.

Perch affords us good examples of the former kind. On this slide are three scales from the body of this fish : the one on the left side is taken from the back (a) : the middle one from the lateral line (b) ; and the one on the right from the belly (c). In order to understand these objects, we must remember that the scales of Fishes are horny or bony plates, developed in the substance of the proper skin, with a layer of which they are always covered. In most cases (as, for example, the Perch), the hinder end of each scale projects, carrying with it the thin layer of .skin with which it is invested ; and thus the scales overlav one another, like the tiles of a house, or like the feathers of a bird, and that for a like purpose. For as the rain, c

falling on the housetop, has a tendency to flow downwards, from gravitation ; and as the slope of the roof is in that direction, the current passing over each tile is deposited from its bottom-edge on the middle of the next, whence it still flows down to the free edge,— and so in succession. So the motion of the bird through the air, and of the fish through the water, produces the very same effect as if these fluids were in motion, and the animals were still ; and therefore the bodies of the latter are, as it were, tiled with feathers or scales, the free edges of which, looking in the opposite direction to the coming of the current (that is, the same direction as its flow), deposit the successive particles of the moving fluid in the midst of the successive feathers or scales. Thus two results ensue, both essential to the comfort of the animal : first, the air or water does not run upward between the feathers or scales to the skin ; and secondly, the surface presents no impediment to free motion. This latter advantage will be appreciated, if you take hold of a dead bird by the legs, and push it rapidly through the air tail foremost : the feathers will instantly rise and ruffle up, presenting a powerful resistance to movement in that direction.

These scales of the Perch have their hinder, or free edge, set with fine crystalline points, arranged in successive rows, and overlapping, Their front side is cut with a scolloped pattern, the extremities of undulations of the surface that radiate from a common point behind the centre. These undulations are separated by narrow furrows, across which, contrary to the ordinary rule, the close-set lines that follow the sinuosities of the outline are not visible. Under the microscope they look as if they had been split in these radiating lines, after the whole number of layers had been completed, and the fissures had then been filled with new transparent substance.

The middle scale is, as I have said, from the lateral line. Along each side, in most fishes, may be observed a line, known as the lateral line, formed by scales of peculiar form. They are commonly more bony than the other scales, and are pierced by a tubular orifioe for the escape (as is generally supposed, though this has been denied) of a mucous secretion, which is poured out from glands beneath, and thus Hows over the body for the double purpose of protecting the skin from the macerating influence of the surrounding water, and of diminishing friction in swimming.

Let us now look at some scales of the cycloid kind. The great majority of our fishes are clothed with such as are of this description. This dead Gold-fish shall give us examples. The three scales in the upper row are from

SCALES OF GOLD-FISH.

the lateral line, the left-hand one (a) taken just behind the head, the second (b) near the middle of the body, and the right-hand one (c) near the tail. Of the lower row, the first (d) is from the back, the second (?) from the middle c 2

of the belly, and the last (f) from the throat. Thus we see there is considerable variety in form presented by the scales even of the same individual fish. They all, however, differ from those of the Perch, in this respect ;—that their free overlapping edges are entire, or destitute of the crystalline points which we saw in the former examples ; while they agree in having the front edges, by which they are during life imbedded in the skin, cut into waves or sinuosities. The lower part, as we now look at them, is the free portion of each, which alone is visible in the living fish, the other parts being concealed by the three neighbouring scales that overlap it,—above, in front, and below.

In those from the lateral line, the tube already referred to is seen to pervade each, running through it longitudinally, so that it opens behind on the outer surface, and in front on the inner or under surface of the scale. In the scales near the front of the line, just behind the head, the tube is large and prominent (a), while in the scales at the opposite extremity it becomes slender ; diminishing, in the very last scale, viz., at the commencement of the tail-fin, to a mere groove.

The whole surface of each scale, when viewed under a lens of low power, is seen to be covered with concentriclines, following the irregular sinuosities of the outline. These lines are the edges of the successive layers of which the scale is believed to be composed, each layer being added in the process of growth to the under surface, and each being a little larger every way than its predecessor; thus the scale is a very depressed cone, of which the centre is the apex. There is a marked difference (indicated in the figures) between that part of the surface which is exposed, and that which is covered by the other scales : the concentric marks in the former are much coarser and less regular, often being interrupted, and seeming to run into each other, and frequently swelling into oval scars. This may, perhaps, be owing to the surface having been partially worn down by rubbing against the gravel of the bottom, or against other objects in the water. Besides the concentric lines, there are seen on many of the scales, especially those of the lateral line, radiating lines varying in number from one to twenty, or more, diverging from the centre towards the circumference, and frequently connected by cross lines forming a sort of net-work around the centre (see c). Under the microscope, these lines appear to be elevated ridges, dividing the coni fiitric lines ; but of their use I am ignorant.

What I have just stated is the ordinary explanation of these hoe concentric lines ; but a careful examination of the structure with much higher powers than we have been using, induces me to doubt its correctness. Reverting to the scales of the Perch, let us notice the clear diverging bands, which look as if the whole scale had been split in several places, and the openings thus made filled with uniform clear substance. The same structure is seen in many other scales, as in this cycloid SCALE OF FLOUNDER. a. Natural size. one from the Flounder which, beinof coarse! v lined, shows the structure well; or i n these from the Green Wrasse. I will now apply to one of these a power of 600 diameters, concentrating the light thrown through the scale from the mirror by the achromaticcondenser,* and examine the scale anew. You now see two distinct layers : the upper one which bears the concentric lines, and a lower clear one which not only fills the

' Called achromatic, from its being so constructed as not to split the li'dit coming through it and cause colour. The term is tunned from the Creek a, k<>L Yptoua (chroma), colour.

radiating bands, but underlies the whole of the lined parts. The concentric lines of the upper layer do not now appear to be edges of successive plates, but irregular canals running through the solid substance. This, however, is deceptive : for, by delicate focussing, we perceive that each portion marked by these lines is really in a different plane from the others, that the highest is at the centre of radiation of the scale, and that each is successively lower till we reach the margin. But now, if with very sharp scissors we cut one of these scales longitudinally through the centre, and examine the cut edge, we find that each of these lines forms a distinct ridge. On the other hand, the under layer of clear substance is quite smooth, and always a little exceeds the margin of the concentrically lined portion. The clear substance that tills the radiating slits agrees both in texture and level with this lower layer, and is manifestly continuous with it.

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