and spiny ant-eater, in which the angle of the jaw is nevertheless not inflected. He did not know that he might have found the inflected angle of the lower jaw, and that he might have been quite right in his conclusion that the animal was a Marsupial; and yet, on laying bare the pelvis, he might have found no 'marsupial bones.' It is known, namely, that in certain living Marsupials (the Thylacinus of Tasmania) the 'marsupial bones' do not become converted into bone, but remain permanently in the condition of cartilage. These structures would therefore be absent in any fossil specimen of such a Marsupial, since cartilages are not preserved in the fossil state. Hence, it is possible, though not probable, that we might some day meet with the skeleton of some extinct Marsupial, in which we should find the angle of the lower jaw to be inflected, but which would nevertheless show no traces of 'marsupial bones.'

In the third place, in any two correlated organs it is not usual that each is correlated with the other, but that one of the two is correlated with the other. That is to say, of any two correlated organs, A and B, it may be true that A is never found without B, but it does not follow that B may not occur without A. Thus, the presence of a stomach adapted for 'rumination' is invariably associated with an imperfect development of the incisors of the upper jaw, the central upper incisors being always wanting; but it is not the case that an incomplete condition of the upper incisors, or the absence of the central ones, is necessarily correlated with the habit of chewing the cud. The proper way of putting the case is to assert that certain structures (A) are never found apart from other

structures (B), though the latter may be present without the former. When, therefore, we find a lower jaw having its angle 'inflected,' we may, with our present knowledge, assert that the animal to which that jaw belonged must have possessed 'marsupial bones' or 'marsupial cartilages' upon the brim of the pelvis. If, however, we were to find a pelvis with marsupial bones, we should not be justified in asserting that the owner of the same must have possessed an inflected angle to the lower jaw. On the contrary, we know that such an assertion would be erroneous, since the 'marsupial bones' are present in the duck-mole and spiny ant-eater, in which the angle of the jaw has its usual form.

RETROGRESSION.

SWAINSON AND THE CIRCULAR CLASSIFICATION.

WE have now considered the main features of the work effected by Cuvier in zoology, and we have next to take a glance at the retrograde and in all respects singular system known as the Circular Classification. The original author of this system was William Sharpe Macleay, a well-known and able entomologist, and the first complete exposition of his system is to be found in a very rare work entitled 'Hora Entomologicæ,' published in London in the year 1819. Though Macleay was the inventor-the term may be used advisedly without disparagement of his undoubted talents and perfect good faith-of the 'Circular System' of classification, Swainson, the well-known ornithologist, was its principal expositor; and it is therefore most suitable that we should consider this system in connection with the latter rather than the former naturalist. In the first place, then, let us take a glance at Swainson's life as told by himself.*

William Swainson was born in October 1789, his father

*Cabinet Cyclopædia: Biography of Zoologists,' pp. 338-352.

being an official in the Custom-house.

His ancestors had

been for generations 'statesmen' in Westmorland, and had lived on their property near Hawkshead; but the family estate had gradually passed into other hands. Swainson was brought up by his father with a view of entering the Custom-house, and his early education was cut short, in consequence of his having an impediment in his speech which entirely prevented him from studying languages, and also because he does not appear to have had 'the least aptitude for the ordinary acquirements of schools.' Hence, we find him at the age of fourteen as junior clerk in a secretary's office in the Customs, with a salary of £80 a year. He had, however, a passion for natural history, a rooted dislike of official trammels, and a burning desire to travel. After he had been about three years a clerk in the Customs, his father obtained for him, in 1807, an appointment in the commissariat department of the army, and in the spring of the same year he was despatched to join the Mediterranean army in Sicily. Here he remained several years, and as his duties were light, he was able to wander all over Sicily, collecting animals and plants, and also to visit Greece. Subsequently he was quartered in Italy, first in one city, and then in another; but his health became impaired, and in 1815 he was sent home on sick leave.

Swainson had now risen to the rank of assistant commissary-general on the staff of the Mediterranean army, and as he was only twenty-six years old, he might have expected much higher promotion had he remained in the service. He had, however, never taken kindly, as some men never do, to official life. He could not even endure

the restraints of English society. 'I had,' says he, 'to join dinner-parties, drink wines which I detested, ride in carriages, dance at balls, and do a hundred other things for which I had neither health nor inclination.' His old passion for foreign travel returned irresistibly upon him. He gave up his appointment in the army, and went upon half-pay. At first he thought of visiting Cape Colony; but hearing that the traveller Burchell had just returned thence with a collection of objects of natural history which filled two wagons, he rashly concluded that there would be nothing left for him to collect there, and he abandoned his intention. It happened however, that at this time Mr Koster, who had formerly travelled in Brazil, and had published an account of his travels, was about to return to that country; and Swainson forthwith made up his mind to accompany him. After some time spent in South America, travelling about and making zoological collections, Swainson returned to England, and settled down to study his collections and describe the results. He was shortly thereafter elected a Fellow of the Royal Society, though he does not seem to have met otherwise with much encouragement. With characteristic energy, he determined to learn the then newly introduced art of lithography, and to see how far this process could be utilised in the production of plates of animals suitable for colouring. His attempts in this direction proving successful, he issued a series of descriptions and figures of new, rare, or remarkable animals, under the title of 'Zoological Illustrations.'

Swainson now settled in London, where he worked hard for two or three years, and followed up his former attempt