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under conditions which vary in the degree of temperature required for congelation, as oil,' 'marrow,' 'lard,'' spermaceti,' suet.' The most solid fats when subject to pressure afford some fluid oil, termed elaine,' and when the fluid fats are cooled to about 32° they deposit a concrete element called 'stearine:' the temperatures of congelation indicate the varying proportions of elaine and stearine. Whether or not it be in relation to the degree of cold to which the hoofs of some ruminants are subject, in traversing the snows of arctic climes, the oil called neat's foot' owes its use in the arts to its maintaining its fluidity below the freezing point. Blubber-oil, which becomes lardy at 45° or 50° Fahr., and is fluid above 55°, most abounds in the thick subcutaneous tissue of the Cetacea. The fat of the hog-tribe, horse-tribe, most Lissencephala, Carnivora, Quadrumana, and Bimana, is in the state of lard.' It exists as suet and tallow in Ruminants. Spermaceti is peculiar to the Cachalot whales (Physeter, Euphysetes).

Some Rodents, the Hare, e.g., show little or no fat; but it occasionally accumulates in the tame Rabbit. In many Rodents it is limited to the abdominal cavity and its special peritoneal processes. In the Seal-tribe and Whale-tribe, on the contrary, there is no fat in the abdomen, or in the mesenteric or omental duplicatures of the lining membrane. The subcutaneous areolar tissue to which it is limited in these aquatic mammals has a coarser reticulate structure in the Seals, the Grampus, and Balancptera, than in the Porpoise, Sperm-whale, and Balana. In all Cetacea the containing tissue is finer upon the trunk, and coarser toward the tail. Fat is subcutaneous in the Hog and human subject, but is also present in the great serous cavities, intermuscular spaces and joints, in variable degrees.

Fat is to the adult what milk is to the young-a source of nourishment when no other is available. Certain Bovines of the tropics, where during the rainy season luxuriant grasses abound on plains parched up in the dry season, accumulate fat and other assimilable substances in a dorsal hump at the period of plenty, and absorb its contents during that of drought. The Camels, when their food abounds, store up similar superabundant nutritious matters in one (C. dromedarius) or two (C. bactrianus) larger humps: whereby they are able to endure unusual fasts by resubstance common to every class of matter.' xx. vol. iii. p. 209. The ternary compounds of carbon, hydrogen, and oxygen, discovered in the condition of petroleum and its allies, in mineral strata, are suspected, with good reason, to have originated in organic bodies.

absorbing those accumulations; concluding their journeys across the desert with the special stores of fat much reduced. Similarly, in other Mammals, when the digestive function and appetite are in abeyance, as in disease, or when food is withheld or scarce, the general fat is absorbed to support the actions of the machine.' Hence the need of accumulations of this nutritive material in torpid mammals prior to their falling into that state, as in Marmots, Hedgehogs, &c. The subcutaneous fat, which forms a thick layer in October, becomes thin in March, yet remains after the fat of the abdomen, mesentery, and about the kidneys has quite disappeared; suggesting, as Jenner remarks, that the external fat also serves as a defence against cold. The subcutaneous wrap of blubber in the naked Cetacea, serves as the non-conductor of heat, in place of hair.

In Physeter portions of spermaceti occur in the general subcutaneous blubber, but the main bulk is stored in the vast supracranial basin, in cells of areolar tissue, strengthened by aponeurotic partitions. The purest spermaceti lies in the smallest and most delicate cells: it is the stearic constituent in excess which crystallises on cooling. For economic purposes these masses are separated by pressure in woollen bags from the elaine, then washed with a weak solution of caustic potash, melted in boiling water, and strained. Thus prepared for commerce spermaceti appears as semi-transparent brittle masses of a foliate fracture, soapy to the touch, with a slight odour and greasy taste: its specific gravity is 943; it fuses at about 114°; thep urified crystalline scales deposited from a solution in boiling alcohol, form 'cetine.' From the blubber of species of Delphinus a peculiar fatty principle called phocenine' is obtained. The characteristic colour of goats' fat is associated with a principle called 'hircin.' With ordinary stearine a variable proportion of margarine' is always combined, and both these and 'elaine' are compounds of a distinct fatty acid with the sweet principle called 'glycerine.' 1 xx. vol. iii. p. 213.

Ib. p. 216.

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CHAPTER XL.

GENERAL CONCLUSIONS.

§ 422. Biological Questions of 1830.-At the close of my studies at the Jardin des Plantes, Paris, in 1831, I returned strongly moved to lines of research bearing upon the then prevailing phases of thought on some general biological questions.

The great Master in whose dissecting-rooms, as well as in the public galleries of Comparative Anatomy, I was privileged to work, held that species were not permanent:' and taught this great and fruitful truth, not doubtfully or hypothetically, but as a fact established inductively on a wide and well-laid basis of observation, by which, indeed, among other acquisitions to science, Comparative Osteology had been created. Camper and Hunter 2 suspected that species might be transitory; but Cuvier, in defining the characters of his Anoplotherium and Palæotherium, &c., proved the fact.

In this truly scientific labour the law of the subordination of the different organic characters to the condition of the whole animal was first appreciated, clearly enunciated, and its application shown to the reconstruction of lost species from fragmentary remains. The importance of this generalisation may be paralleled with that of the principle of equivalents in chemical science.

Of the relations of past to present species, and the conditions of their succession, Cuvier had not an adequate basis for a decided opinion. Observation of changes in the relative position of land and sea suggested to him one condition of the advent of new species on an island or continent where old species had died out. This view he illustrates by a hypothetical case of such succession, but expressly states:- Je ne prétends pas qu'il ait fallu une création nouvelle pour produire les espèces aujourd'hui existantes, je dis seulement qu'elles n'existoient pas dans les mêmes lieux, et qu'elles ont dû y venir d'ailleurs."4

3

Geoffroy Saint-Hilaire, whose discussions with his colleague in the Académie des Sciences' made its annals of 1830 memorable,

2

equally rejecting the idea of new creations,' opposed to Cuvier's inductive treatment of the question the following expression of belief:-' Je ne doute pas que les animaux vivants aujourd'hui ne proviennent, par une suite de générations, et sans interruption, des animaux perdus du monde antédiluvien.' But with regard to the demonstration of the proposition, of the truth of which he could not entertain a doubt, Geoffroy Saint-Hilaire expressly states: Je crois que les temps d'un savoir véritablement satisfaisant en géologie ne sont pas encore venus.'

The main collateral questions argued in these debates, to some of which I listened, and to all the reports and consequent pamphlets relating thereto devoted intense attention, appeared to me to be the following:

Unity of Plan or Final purpose, as a governing condition of organic development?

Series of species, uninterrupted or broken by intervals?
Extinction, cataclysmal or regulated?

Development, by epigenesis or evolution?

Primary life, by miracle or secondary law?

On returning home and resuming office with additional duties at the Royal College of Surgeons, I was guided in all my work with the hope or endeavour to gain inductive ground for conclusions on these great questions.

§ 423. Homology or Teleology? Teleology? Cuvier held the work of organisation to be guided and governed by final purpose, or adaptation, expounding this principle under the terms conditions of existence' and 'correlations of structure.' Geoffroy denied the evidence of design, and protested against the deduction of a purpose as, e. g., from the coexistence of a valve with a definite course of fluid: he contended for the principle which he called 'unité de composition,' as the law of organisation. Most of his illustrations were open to the demonstration of inaccuracy, and his arguments to the refutation which they received from Cuvier in the debates in question: the logic, and, as it seemed, the facts, were on the side of teleology. The figurative language, moreover, in which contemporary anatomists had expressed their views of a principle akin to Geoffroy's was ill-calculated to enlist supporters. The expressions by which disciples of the school

'Or, cette proposition, déja contraire aux plus anciennes données historiques, répugne tout autant aux lumières de la raison naturelle qu'aux spéculations plus réfléchies des sciences physiques.'-CCLXXXVII". p. 210.

? Also, more decisively:-Les animaux perdus sont, par voie non interrompue de générations et de modifications successives, les ancêtres des animaux du monde actuel.' -CCLXXXVII". p. 208.

of Schelling illustrated, in the animal structures, the transcendental idea of the repetition of the whole in every part,' operated disadvantageously to the calm enquiry into the prime question at issue. To Cuvier this language seemed little better than mystical jargon, and he alluded to it with transparent contempt.' When he did extend inferences from comparative anatomy beyond the adaptation of structure to function, Cuvier went not beyond a recognition of what I have since termed special homologies': 2 and this lowest degree of correspondence he explained on the ground of the subserviency of such homologous parts to similar ends in different animals; 3 viewing them, in fact, in that relation which I express and contrast by the term ' analogies.' With Cuvier answerable parts occurred in the zoological scale because they had to perform similar functions.

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Most of my fellow-students at the Garden of Plants, in 1830, and some subsequent fellow-labourers, Johannes Müller, Rud. Wagner, Milne-Edwards, Agassiz, implicitly accepted this explanation of the fact of answerable bones and other parts occurring in different species.

After the publication of the Memoir on the Pearly Nautilus,' and of those on Monotrematous and Marsupial generation, which subjects Cuvier had strongly recommended to my attention, the question of the condition or law of special homologies pressed itself upon me, more especially in connection with the task of arranging and cataloguing the osteological part of the Hunterian Museum.' As my observations and comparisons accumulated, with pari passu tests of observed phenomena of osteogeny, they enforced a reconsideration of Cuvier's conclusions to which I had previously yielded assent. To demonstrate the evidence of the community of organisation, I found that the artifice of an archetype vertebrate animal was as essential as that of the archetype plant had been to Goethe in expressing analogous ideas; and as the like reference to an ideal type' must be to all who undertake to make intelligible the unity in variety' pervading any group of

Quant à M. Oken, il déclare les pièces en question les parties écailleuses des temporaux, ou, selon son langage mystique, "la fourchette du membre supérieur de la tête."-Cet humerus de la tête de M. Oken devient pour M. Spix le pubis de cette même tête; ou, pour parler un langage intelligible, un des osselets de l'ouie, savoir le marteau.'-CXXXIX. tom. v. 2o partie, p. 85.

2 CXL. p. 7.

Ce n'est qu'un principe subordonné à un autre bien plus élevé et bien plus fécond, à celui des conditions d'existence, de la convenance des parties, de leur coordination pour le rôle que l'animal doit jouer dans la nature. Voilà le vrai principe philosophique d'où découlent la possibilité de certaines ressemblances.'-ccxciv", p. 9. ♪ XLIV.

1 CXL. p. 7.