into existence,—in which that most wonderful feature of its organisation, the feather, arose out of the scaly covering of its Reptilian ancestors,-in which its heart came to be divided into four chambers instead of three, and the arrangement of its blood-vessels altered accordingly, in the establishment of the complete double circulation,' that insures the perfect aëration of the blood needed for the maintenance of the extraordinary muscular energy by which the feathered wings can sustain the body in flight, -I cannot see that "natural selection" throws the least light. There is, as I have already pointed out, an adaptation in the several parts of the structure of the Bird, not only to one general result, but to a consentaneous action in bringing about that result, which shows itself to be more complete, the more closely it is scrutinised. And on the hypothesis of "natural selection" among aimless' variations, I think it could be shown that the probability is infinitely small, that the progressive modifications required in the structure of each individual organ to convert a Reptile into a Bird, could have taken place without disturbing the required harmony in their combined action; nothing but intentional prearrangement being competent to bring about such a result. And the point on which I now wish to fix your attention, is the evidence of such pre-arrangement that is furnished by the orderly sequence of variations following definite lines of

advance.

6

I shall illustrate this, in the first place, by a general outline of a Memoir which I last year presented to the Royal Society, in which I embodied the final results (as relating to this subject) of an inquiry on which I had been engaged for forty years into the organisation of the Foraminifera; a group of marine animals of the simplest protoplasmic nature, which yet form for themselves shelly coverings of singular regularity and complexity of structure, the aggregation of whose remains forms many important Limestone-strata (as the Nummulitic limestone of which the Pyramids are built, and the Miliolite limestone which has

furnished the chief building material of Paris), whilst Chalk is a product of their disintegration. My studies of this group began with a comparatively gigantic type called the Orbitolite; which is a shelly disk, sometimes attaining the diameter of an inch, living at the present time on the coast of Australia, the Fiji reefs, and other Pacific shores, and found fossil in the early Tertiary limestones of the North of France, one bed of which is in great degree formed of an accumulation of disks very similar to those now piling

Shelly Disk of Orbitolites complanata, showing concentric rings of chamberlets, arranged round a central nucleus.

themselves up near its Antipodes. I was supplied, moreover, with a series of smaller disks (chiefly picked out of shore-sands), down to an almost microscopic minuteness, but agreeing with the larger in this fundamental feature of their structure,-the arrangement of their mutually connected' chamberlets' in successive circles round a central 'nucleus,' their plan of growth being thus cyclical. This plan is most fully carried out in typical specimens of the

FIG. II.

large Orbitolites complanata (Fig. I); in which the sarcodic nucleus,' consisting of a flask-shaped 'primordial segment,' a, Fig. II., and of a circumambient segment,' b, b, c, is at once surrounded by a complete ring of sub-segments, separately budded-off from it; successive rings, with constantly increasing numbers of sub-segments, being in like manner budded-off around the outer border of their predecessors, sometimes to the number of 100. The shell, moulded upon this composite body, thus acquires the very regular discoidal form shown in Fig. I.; and its vertical thickness usually increases from its centre towards its circumference. A vertical section of the disk (Fig. III., 2) shows that the chamberlets visible on its two surfaces form two superficial layers, which communicate with continuous annular galleries that lie just beneath them (Fig. III., 3, d', d'), every chamberlet, a, opening at each end into one of these galleries; whilst the intermediate part of the disk is occupied by columnar chamberlets (b, b), which open at either end into the annular galleries, and are connected with each other by several ranges of oblique passages (e, e, f, f). The passages proceeding outwards from the last-formed ring, open on the margin of the disk as pores arranged in more or less regular vertical series (Fig. III., 1); and these pores constitute the only means of communication between the complicated cavitary system of the disks, and the surrounding waters from which the animal that inhabits them draws its nutriment. The substance of this animal is apparently altogether protoplasmic. Notwithstanding this complexity in the structure of the disk, there is not the least trace of differentiation in the contents of the several series of chamberlets. On the contrary, there is every reason to believe that a continuous interchange must be always going on between the proto

plasmic substance of the central and that of the peripheral parts of the disk; so that the nutriment taken in by the pseudopodial' extensions which the latter puts forth through the marginal pores, may be diffused through the whole multiple series of sub-segments, of which the body

Structure of Shelly Disk of Orbitolites complanata.

1. Edge of Disk, showing multiple series of marginal pores.

2. Vertical Section, showing two superficial planes of chamberlets, separated by intermediate columnar structure.

3. Internal Structure:-a, superficial chamberlets; b, b, columnar chamberlets of intermediate layer; c, floors of superficial chamberlets, showing the opening at each end into the annular gallery beneath; d, annular galleries cut transversely; d', d", annular galleries laid open longitudinally; e e, ff, oblique stolon passages of intermediate layer.

of this organism consists. This I characterised as the complex' type of Orbitolite structure.

The minute disks picked out of shore-sands, however, were found to present a much simpler plan of structure; the chamberlets being arranged in a single plane around the central nucleus, those of each ring being connected by a single annular gallery, and their openings at the margin

1. Surface of Disk, showing later growth of concentric rings of chamberlets around a first-formed spire.

2. Central portion enlarged.

3. Edge of Disk, showing single row of marginal pores.

4. Vertical Section, showing succession of chamberlets communicating with each other radially by passages in the annular partitions, and laterally by the annular canals, whose sections are seen as dark spots.

The

forming but a single row of pores (Fig. IV., 1, 3, 4). arrangement of the first-formed chamberlets, moreover, presented a singular departure from the cyclical plan, showing a distinctly spiral disposition (Fig. IV., 2); the