the segmentary structure of an arthropod. But they may suffice. to introduce notable variations in a species, more particularly when transmitted by hereditary descent.

COROLLARY.

The last three Propositions afford a practical answer to the problem suggested in the second Corollary to the hundred and eightyserenth Thesis. In that Corollary it is concluded, that a true classification of material substances-in particular, of living bodies -must be based on the nature and diversities of their substantial Forms. But the difficulty is at the same time proposed, that these Forms, like the matter, are not subject to the perception of the senses; how then can we make use of them for purposes of classification? Is there any way in which they reveal themselves to human cognition? The answer is now evident. The substantial Form of a material substance reveals itself to sensile perception and becomes consequently object of cognition, in four different ways: by its natural operation; by its generic and specific properties; in particular, by its bodily composition or organization; lastly, by its natural accidents. Let us consider each one of these apart, in order to see whether we may not be able to get at certain practical rules to guide us in classification; premising that the revelations proceeding from these four sources are unequal in their evidence, and that in this respect they follow the order just indicated.

i. First in order of certainty comes the natural operation of a material substance, that native energy by which it pursues in act and attains its appointed end. In living things, (and to the consideration of these the present Corollary is intentionally restricted), this natural operation will, of course, differ according to the different kinds of life,-i e. of substantial Forms,-which manifest themselves in these operations. In plants it is limited to growth, nutrition, reproduction; in animals, besides these just named which they share with plants, there are to be found sensation, imagination, instinct, habits, and in certain higher orders of animals, obumbrations of intellect and will. In man, over and above all these which he shares in common with plants and animals, there are the purely spiritual acts of intellect and will, made known to us by language spoken and written, and in many other ways.

The Angelic Doctor remarks that the first and most rudi

mentary sense in animals is that of touch. If this, therefore, is present, we may be sure that the living thing is an animal, not a plant; even should the other senses be wanting.

ii. Next to the natural operations, the generic and specific properties most clearly reveal the nature of the substantial Form; because, though no part of the essence, they flow from it and invariably accompany it. Thus, for instance, that a plant is dioecious, monoecious, or hermaphrodite, that it is terrestrial, aquatic, marine, that it is exogenous, or endogenous, that it is evergreen or deciduous, all these properties seem to be of higher importance, and to reveal more about the nature and substantial Form of a plant, than the mere number of its stamina, or the composition of its corolla. So, again, man's capacity for laughter is a more certain indication of his specific nature than his possession of a vertebral column or the fact that he has two hands.

iii. Inferior to the two former, but still of considerable service in helping to the discovery of the specific nature of a plant or animal, are the material structure and organism, which are foremost among the natural accidents. These are chiefly useful in enabling us to determine more easily the natural operation and properties of the entity. Thus, for instance, the baleen-plates, the fins, the spiracles, of the whale seem to reveal more of the specific nature of the animal, of its essentially oceanic life, than its possession of mammary glands or of some hairs upon its skin; consequently, the former characteristics of the cetacea are naturally of much higher value in a really scientific classification than the latter. On the other hand, a division which is based on the form and proximity of the nostrils and on dental formulae, such as that of the quadrumana into strepsirhina (or twisted nostrils), platyrhina (or wide-set nostrils), and catarhina (or oblique and near-set nostrils), is trivial and unscientific. For the above reasons, organization is of much higher value than mere structure; for the former is more intimately connected with natural operation. This observation particularly applies to the organs of sense. Professor Haeckel, in calling attention to the two primary germ-layers, constituted subsequently to the egg-cleavage, tells us, it may be remembered, that the outer layer (or ectoderm) 'gives rise to the animal organs of sensation and movement, the skin, the nerves, and the muscles;' while from the inner layer (or endoderm) 'the vegetative organs of nourishment and reproduction, the intestine and blood-vessel system in parti

cular, arise1.' Yet, strange to say, it is prominently from these latter, and from the inferior parts of these latter, that modern classification has borrowed its principles of differentiation; and not from the development of the exoderm which is the specific source of animal organism. Let it be permitted to illustrate the remark here made by an example. Those who have studied modern books on comparative anatomy as well as on the theory of evolution must have had their attention repeatedly called to a fish that has lately gained for itself a great, though perhaps unmerited, reputation. This fish is the amphioxus, or lancelet, (so called from its lanceolate shape),-a species of lamprey that lives buried in sandbanks. This animal is skull-less,-has no formed brain,-no organ of hearing, only rudimentary eyes, (if they can be called such), a very doubtful organ of smell,—has no distinct heart or developed system of circulation, no lymphatic system,-no skeleton,-imperfect organs of reproduction; yet, according to the classification now in vogue, this, one of the lowest forms of integral animal life, finds a place,above ants, termites, bees, trap-door spiders,-in the highest of the constituted Sub-kingdoms, because it possesses a notochord, the supposed rudiment of a vertebral column. Professor Haeckel justifies this strange appointing in words strikingly illustrative of the matter in hand. He tells us, that in the History of Evolution' and in comparative anatomy, 'the head with the skull and the brain are non-essential, as are also the extremities, or limbs. It is true that these parts of the body possess a very high—even the very highest physiological importance; but for a morphological conception of the Vertebrate, they are non-essential, because they appear only in the higher Vertebrata, and are wanting in the lower,' that is, so far as skull and brain are concerned, in the Lancelet alone, and in no other. The lowest Vertebrates possess neither a clearly marked head with a brain and skull, nor extremities, nor limbs. . . This single lowest Vertebrate, which deserves the closest consideration, and, next to Man, must undoubtedly be called the most interesting of all Vertebrates, is the well-known Lancelet, or Amphioxus 2.'

Now, any classification which is exclusively derived from matter must be necessarily deficient and exposed to error for three principal

1 Evolution of Man, Ch. viii, Vol. I, p. 196. The italics in this and the following quotation have been introduced. They are not in the original.

2 Ibid. Ch. ix, Vol. I, p. 253.

reasons.

First of all, some substantial Forms rise above the matter or bodily structure in their essence; others after a manner, as has been pointed out in the last paragraph of the hundred and ninetieth Proposition. In such cases the structure, and even organization, -of the body would give but a very imperfect and partial knowledge of the specific nature. Then, again, there may be modifications of bodily structure and organism, which are either individual, as in the lancelet, or particular, that is to say, common to a group under the same species, such as the abdominal pouch of the marsupials. These variations may be considerable, and the study of them always interesting; but they do not form any part of the specific nature. Thirdly, similar variations may be purely accidental, and arising from extrinsic causes; but these have no direct connection with the specific nature. Yet Dr. Nicholson tells us, that Philosophical classification is a formal expression of the facts and laws of Morphology and Physiology,'-terms not happily chosen, but which the author explains to mean, that It depends upon a due appreciation of what constitute the true points of difference and likeness amongst animals, and we have already said that these are morphological type and specialisation of function ','-the structure and organism of bodies, in plain language. The pages that immediately follow are a sorrowful comment on these philosophical claims.

It is plainly deducible from the above animadversions, that in animals the organism is much more closely connected with, and indicative of, the Form and specific nature than is the structure. Of organisms the most important are the organs of sense and all else that pertains to the nervous system.

iv. From what has been already said it is sufficiently plain, that accidents may be useful in enabling us to signalize variations and to distinguish with greater accuracy between these and true species, but have no place in classification of species. Of such are colour, more or less covering of hair, possession and size and shape of horns, make of the nose, number and position of fins, etc.

PROPOSITION CXCII.

Within the periphery of the entire cosmic order there are four primary gradations of substantial bodily Forms. In the lowest grade are such as constitute inanimate, in the second

Manual of Zoology, General Introduction, n. 9, p. 18. See pp. 19-23.

such as constitute vegetable, in the third such as constitute animal, substances. The fourth and highest grade embraces the created soul of man.

Since this Proposition has been allowed a place in the present series as introductory to those which are about to follow, yet mainly in order that the doctrine of the Angelic Doctor touching the subject-matter of this Article may be fully exposed; a statement of St. Thomas shall supply the place of a declaration. The following are his words: Although the being of Form and matter is one,' since they co-exist in the composite; nevertheless, it is not necessary that the matter should be on a par with the Form in being. On the contrary, by how much the Form is nobler, by so much does it always surpass matter in its being. This is plain to any one that examines into the operations of Forms, from the consideration of which we get to know the nature of the Forms; since everything operates according to its being. Hence, a Form whose operation exceeds all material conditions, itself too, in proportion to the dignity of its being, superexceeds matter. For we find certain lowest Forms which are capable of no operation, save that to which those qualities attain which are dispositions of matter; such as hot, cold, wet, dry, rarified, dense, heavy, light, and the like. Such are the Forms of the elements.' It should be noted that the particular qualities here enumerated have a special connection with the elements supposed to be such according to the physics of the time; but this does not in any wise affect the truth of the distinction. With another list of qualities which, in accordance with its supposed elements, modern chemistry could supply, this observation of the Angelic Doctor would hold equally good. St. Thomas continues: Hence, these are Forms altogether material, and totally immersed in matter. Above these we find the Forms of mixed' (chemically combined) 'bodies, which, albeit they do not extend to any operations that cannot be effected by virtue of the aforesaid qualities, nevertheless sometimes operate these effects by a higher bodily virtue. . . . Above these, again, we discover some Forms whose operations are extended to certain effects that exceed the virtue of the aforesaid qualities; though the aforesaid organic qualities assist in the operations of these Forms. Such are the souls of plants, which are assimilated not only to the powers of the heavenly bodies by their surpassing the active and passive qualities' of the elements, but are assimilated even to those who impart to