tain parts of animals can, in the ordinary course of events, have any reasonable chance of being preserved as fossils; and furthermore, that only certain deposits, such as mud, are capable of preserving these remains uninjured. "The crust of the earth," to quote from Darwin, "with its embedded remains, must not be looked at as a well-filled museum, but as a poor collection made at hazard and at rare intervals." We also, however, saw that in spite of this imperfection of the record, several series of fossil links have been obtained; notably, in the cases of the horse and Paludina; and that the Archæopteryx is one of the most important links known.

A further consideration in regard to fossil links is that of the unlikeness between the dominant forms of one age and those of succeeding ones: for instance, between the reptiles of the secondary period and the later forms. Undoubtedly, if we regard these alone, there are great and apparently abrupt gaps; but we must not suppose fossil forms all to stand in the direct line of ancestry of living animals.

As it has been with animals, so it has been with men. As we find in human history the Egyptian, Greek, and Roman nations, each in turn dominant, so also do we note that they are not lineal descendants one of another, but collateral branches of the great human family or tree, which in succession attained maturity and gained dominion. Dominant races of animals in successive geological ages have often died out and left no descendants-great reptiles such as

the Dinosaurus for example. It will be these dominant races which will be the most likely to leave fossil remains as with the buildings and records of man-and, especially if of large size, to give character to the age. Yet these do not usually stand in the direct line of ancestry of living forms, which are descended from collateral branches, which at those times were insignificant. This consideration explains at once the apparently sudden gaps, and the difficulty in obtaining evidence of actual ancestors. Dominant types often die out, and are succeeded by others whose early history is difficult to unravel, because overshadowed. by the then dominant forms.

On the whole, therefore, the search for links is not so hopeless as it appeared at first sight, when we once realise what a link really is, and what we have to look for. Additions are yearly, or almost monthly, made to our knowledge of the former history of the earth, in the discovery of fossils, now that their true importance is recognised.

Before concluding the subject of missing links it will be well to refer briefly to that aspect of the problem known familiarly as the "monkey question." The Darwinian theory does most undoubtedly imply that there is a blood-relationship between man and the lower animals; and it is also a most undoubted fact that, of these animals, the anthropoid apes-the orang, the chimpanzee, and the gorillaare those which are most closely allied to man. Such being the case, much ingenuity has been exercised in the search for "missing-links" which will bridge over the gap between man and monkey, and very bold statements have been based on the failure of these efforts.

Such ingenuity is, however, misdirected, and such efforts predestined to fail; for if what we have said above as to the real nature of links be true, it follows that the links between man and monkey will most certainly not be directly intermediate forms, any more than the link between the horse and donkey is a mule. From time to time we are provided with such alleged direct links, and it is a source of very legitimate amusement to a Darwinian to note the extreme anxiety people always show to prove that these waifs are really monkeys and not men, and the readiness with which they are able to accomplish this to their own satisfaction. And yet in all cases they have proved to be really human beings after all. Thus, of late years we have had a couple of idiot children spoken of as Aztecs, and a Siamese child called Krao, who differed from the rest of the family in nothing except unusual hairiness; not to mention other celebrities, all of whom were pronounced positively to be monkeys on their first appearance. Indeed, the only conclusion to be drawn from such cases, appears to be how very easy it is to persuade people to believe that human beings are monkeys.

PERSISTENT TYPES.

PERSISTENT TYPES, a group of cases which we have already considered,* have been brought forward

as an objection to the Darwinian theory, on the ground that, as the fittest survive, there should be a continual improvement in the race; whereas, we have seen forms such as Lingula and Nautilus persisting apparently unchanged for periods of enormous duration; or even through the whole time of which we have any evidence in regard to life on the earth. We must bear in mind, however, that natural selection does not necessarily imply advance, and is perfectly consistent with a stationary condition; for the fittest now may be the fittest many years or ages afterwards. It is quite practicable for particular forms to remain stationary for enormously long periods, provided their environment, or at least all features of the environment affecting them, remain constant.

Persistent types are usually marine, for there the conditions are more constant. They are very commonly found on sandy shores, in which they often burrow; their tenacity of life and power of withstanding injury are very great; they are usually also unpalatable, and hence not eaten as food by other animals. Their tenacity of life is well shown in the case of Lingula, which was carried by Morse in his pocket during a three days' journey across America without coming to any harm; and Balanoglossus has been known to live in a bucket of unaërated water in a hot climate, with the hinder part of its body completely macerated, and its branchial skeleton exposed.

The persistence of lowly organised forms alongside more highly organised ones is often felt as a difficulty; for if the higher animals are descended from more lowly constituted ancestors, as we believe, and if these advances, these steps forward have been preserved because they were improvements, and because they gave advantage in the struggle for existence, how is it that we find the lowly organised forms still living alongside the higher and improved ones ?

The answer is that these lowly organised forms occupy places which cannot be filled by the higher forms; as Wallace says: "There is no motive power to destroy or seriously modify them, and they have thus probably persisted, under slightly varying forms, through all geologic time." Again, if we compare human history, we see that advance in civilisation does not involve the advance of all the members. For instance, some shops become larger and more pretentious, yet there are still plenty of places where small shops can survive, while there is no room for large ones. Again, some nations still exist which use bows and arrows, or slings and clubs, which are easily replaced and more suitable for their purposes than more modern implements of warfare.

DEGENERATION, OR RETROGRADE DEVELOPMENT.

It is very commonly assumed that, as in the struggle for existence, the fittest survive; therefore each generation must be rather more highly or more perfectly organised, and fitter to survive than the preceding; and that in all cases there must be a