FIG. VII.

Diagrammatic representation of the transition from the 'simple' to the 'complex' plan of growth, as shown. in vertical section, from the primordial and circumambient chambers (cp c') of the centre, to the margin, whose pores are shown at mp. The chambers m, m1, m3, m3, m', are all formed upon the simple type (as in Fig. IV. 4), and show at ac, ac, the cross sections of the annular canals, which connect all the chamberlets of one ring, and at r, r, r, the radial passages connecting the successive annuli. The chambers d, d', d, are formed upon the duplex type; the annular canals ac, ac, being single, but the radial passages r being double. The chambers e, e', show two annular canals ac, ac', between which is interposed a columnar chamberlet, continuous with the two superficial chamberlets s s'. In the chambers f, f', f, f, to the margin, which are all formed on the fuily-developed complex type, the upper and under superficial chamberlets ss, s' s', are completely cut off from the intermediate columnar portion, and, by a shifting of their position, each is made to communicate with two annular canals.

interval between two annular canals, and communicates with both of them; while the sarcodic body which occupies this cavitary system thus comes to have the more complicated arrangement shown in Fig. VIII. With the increase in the thickness of the intermediate layer, the double row of marginal pores of the 'duplex' type gives place to the multiple series (Fig. VII. mp) of the 'complex.'

Now it seems to me impossible not to recognise the fact, that the evolution of this type has taken place along a definite course; every stage being one of progress, and each being (so to speak) a preparation for the next. This, perhaps, will be most clearly seen by looking at the progressive complication in the structure of the sarcodic body on which the shell is modelled. First, we have a simple pear-shaped particle, extending itself into a cord that lies in a continuous spiral around it, with constrictions at intervals. This spire flattens out; and then, by the formation of transverse partitions, traversed by pores, the successive additions become segmentally separated from each other, though mutually connected by sarcodic extensions. Next, these segments undergo a further division into sub-segments: all those forming each row being strung (as it were) on a continuous sarcodic cord, which connects them laterally; while the successive rows are connected, as before, by radial 'stolon processes,' those of the last-formed row issuing forth through the marginal pores, as the pseudopodia, through which nutriment is absorbed for the entire body. Then, by the opening out of the spire, the lateral connecting cords become complete rings, from which the radial stolonprocesses are given off; and the future increase of the simple' type consists in the formation of new circular series of sub-segments, each strung, as it were, on its own annular cord. Now, the advance towards the plex' type is prepared-for, so to speak, by the sending forth of two sets of radial stolon-processes instead of one;

com

-a change which, taken by itself, is meaningless, since every one who is familiar with the variability of the Rhizopodal type (especially as exhibited in the tran

sitional forms between Peneroplis and Dendritina) knows that it cannot make any difference to the animal whether its pseudopodia issue from the margin of the disk, through a single or through a double row of pores; but which is full of meaning when regarded as a preparation for that splitting of each annular cord into two, in which the transition from the 'simple' to the complex' type essentially consists. Every annulus of the body of the latter consists

of a series of columnar seg-
ments (Fig. VIII., e e, e' e'),
passing at each end into an
annular cord (a a', b b'), and
communicating with the series
internal and external to it,
by oblique stolon - passages,
the number of which is re-
lated to the length of the
columns; this, again, deter-
mining the thickness of the
calcareous disk which is mod-
elled upon them. The sub-
segments of the two super-
ficial layers (c c, d d) do not
communicate with each other;

but those of each circlet are
connected (as already de-
scribed) with the two annular
cords that lie beneath.
by this elaborate arrange-

And

FIG. VIII.

a

Portion of Sarcodic body of Complex Orbitolite :-a a', b b', upper concentric zones; c c, upper layer

and lower annular cords of two

of superficial sub-segments; dd,the lower layer; e e and e' e', intermediate columnar sub-segments of the two zones, giving off oblique stolonprocesses.

ment, every part of the minutely sub-divided protoplasmic body which occupies the minutely sub-divided cavity of these disks, is brought into continuous relation with every other part, and with the peripheral annulus whose marginal pores constitute the only access through which nutriment can reach it from without.

I might further illustrate my argument that we have here the obvious indication of a pre-arranged plan, by

the remarkable provision made, not merely for the reparation of injuries, but for the restoration of the typical form when the disk has been so much broken as to destroy that form completely. Even a broken-off marginal fragment may give origin to a new disk; its sarcodic body extending itself all round it, so as to form a continuous band; and this forming a complete annulus of chamberlets, round which new annuli are successively added.

In the Life-history of the perfected type, then, we can clearly trace a sequence which runs exactly parallel to what we have reason to regard as its Evolutionary history, and, in addition, a provision for the maintenance of the perfected model; the reparative process being carried on-alike in the 'simple,' the 'duplex,' and the 'complex' types-upon the plan characteristic of each.

But my special reason for dwelling upon this 'instance' (as Bacon would call it) is, that the influence of Natural Selection would here seem to be excluded by the fact that the whole series of ancestral forms through which the most elaborately-constructed Orbitolite now existing may be assumed to have passed, continues to live and flourish at the present time. The very same dredging may bring up shells of Cornuspira, constructed upon the undivided spiral plan shown in Fig V., 1; shells of Spiroloculina, in which the spiral is partially interrupted by rudimentary partitions, as at 2; shells of Peneroplis, in which the partitions are complete, but traversed by pores, as at 3; shells of Orbiculina, in which the peneropline chambers are divided into chamberlets, the plan of growth still remaining spiral, as at 4; and shells of the three types of cyclicallygrowing Orbitolites 5, 6, 7. As already stated, the condition of the sarcodic body undergoes no corresponding advance; that of the most complex' Orbitolite being as homogeneous or undifferentiated as that of the simple Cornuspira. There is no evidence whatever of any struggle for existence' or 'survival of the fittest'; all showing themselves equally fit to survive. All

' variation' seems to have taken place in such a definite

direction, as to evolve calcareous fabrics of ever-increasing complexity; but this complexity can scarcely give any advantage to the organisms which have attained it, these being fully as incapable as the simpler forms of escaping from their enemies by movement, and showing no such differences of aspect as would enable them to elude observation. In fact, the Fishes and larger Crustaceans which would probably be their chief destroyers, would be likely to be most attracted by the larger disks of the 'complex' type; while the younger specimens of that type, being indistinguishable except by the Microscopist from full-grown specimens of the 'simple' and 'duplex' types, are not likely to be passed over by any hungry destroyer that might find these latter of more suitable dimensions.

The last remark I have to make in relation to this noteworthy 'instance,' is that its value is not in the least degree lessened by the fact that the evolutionary process seems to be dependent upon Physical agencies. The Orbitolite type (as at present known to us) flourishes best in tropical or sub-tropical seas; the largest 'complex' forms yet discovered being found on the Fiji reefs; while the smallest 'simple' forms only extend as far north as the Mediterranean,-with the singular exception of the deep-sea type found to the west of Ireland, which is probably a survival from the warmer climate of some former epoch. And among the specimens collected by the Challenger on the Fiji reef, I have found a marked difference; all the most highly-developed forms of the 'complex' type having been found near the surface, where the temperature is the highest, and the supply of food most abundant. But it can no more be said that these physical agencies produced the advance, than that heat can make a Chick out of the yolk and white of an egg, without a germ to appropriate and build up these materials. These Physical agencies supply only the conditions required for the evolutionary process,—the source or spring of which is in the Germ itself.