Part 8

Some of the elements in this classification are fundamentally unsatisfactory in that they are based on negative characters. Such is the group of Anaima which is parallelled by our own equally convenient and negative though morphologically meaningless equivalent Invertebrata. Others, such as the subdivisions of the viviparous quadrupeds, can only be forcibly extracted out of Aristotle’s text. But there are yet others, such as the separation of the cartilaginous from the bony fishes, that exhibit true genius and betray a knowledge that can only have been reached by careful investigation. Remarkably brilliant too is his treatment of Molluscs. There can be no doubt that he dissected the bodies and carefully watched the habits of octopuses and squids, Malacia as he calls them. He separates them too far from the other Molluscs, grouped by him as Ostracoderma, but his actual descriptions of the structure and sexual process of the cephalopods are exceedingly remarkable, and after being long disregarded or misunderstood were verified and repeated in the course of the nineteenth century.

The rediscovery and verification of this and other Aristotelian observations is detailed by C. Singer, ‘Greek Biology and the Rise of Modern Biology,’ Studies in the History and Method of Science, vol. ii, Oxford, 1921.

Passing from his general ideas on the nature and division of living creatures we may turn to some of the most noteworthy of his actual observations. In the realm of comparative anatomy proper we may instance that of the stomach of ruminants. He must have dissected these animals, for he gives a clear and correct account of the four chambers. ‘Animals’, he says, ‘present diversities in the structure of their stomachs. Of the viviparous quadrupeds, such of the horned animals as are not equally furnished with teeth in both jaws are furnished with four such chambers. These animals are those that are said to chew the cud. In these animals the oesophagus extends from the mouth downwards along the lung, from the midriff to the big stomach [rumen, or paunch], and this stomach is rough inside and semi-partitional. And connected with it near to the entry of the oesophagus is what is called the kekryphalos [reticulum, or honeycomb bag]; for outside it is like the stomach, but inside it resembles a netted cap; and the kekryphalos is a good deal smaller than the big stomach.’ The term kekryphalos was applied to the net that women wore over their hair to keep it in order. ‘Connected with this kekryphalos,’ he continues, ‘is the echinos [psalterium, or manyplies], rough inside and laminated, and of about the same size as the kekryphalos. Next after this comes what is called the enystron [abomasum], larger and longer than the echinos, furnished inside with numerous folds or ridges, large and smooth. After all this comes the gut....’ ‘All animals that have horns, the sheep for instance, the ox, the goat, the deer and the like, have these several stomachs.... The several cavities receive the food one from the other in succession: the first taking the unreduced substances, the second the same when somewhat reduced, the third when reduction is complete, and the fourth when the whole has become a smooth pulp....’ ‘Such is the stomach of those quadrupeds that are horned and have an unsymmetrical dentition (μὴ ἀμφώδοντα); and these animals differ one from another in the shape and size of the parts, and in the fact of the oesophagus reaching the stomach central-wise in some cases and sideways in others. Animals that are furnished equally with teeth in both jaws (ἀμφώδοντα) have one stomach; as man, the pig, the dog, the bear, the lion, the wolf.’

Historia animalium, ii. 17; 507ᵅ 33.

De partibus animalium, ii. 17; 507ᵇ 12.

Historia animalium, ii. 17; 507ᵇ 12.

A very famous example in the Aristotelian works anticipating modern biological knowledge is afforded by his reference to the mode of reproduction of the cephalopods. ‘The Malacia such as the octopus, the sepia, and the calamary, have sexual intercourse all in the same way; that is to say, they unite at the mouth by an interlacing of their tentacles. When, then, the octopus rests its so-called head against the ground and spreads abroad its tentacles, the other sex fits into the outspreading of these tentacles, and the two sexes then bring their suckers into mutual connexion. Some assert that the male has a kind of penis in one of his tentacles, the one in which are the largest suckers; and they further assert that the organ is tendinous in character growing attached right up to the middle of the tentacle, and that the latter enables it to enter the nostril or funnel of the female.’

Historia animalium, v. 6; 541ᵇ 1. The hectocotylization of the cephalopod arm which is here recorded as an element in the reproductive process of these animals is denied in the De generatione animalium, i. 15; 720ᵇ 32, where we read that ‘the insertion of the arm of the male into the funnel of the female ... is only for the sake of attachment, and it is not an organ useful for generation, for it is outside the passage in the male and indeed outside the body of the male altogether.‘ Yet even here Aristotle knows of the physical relationship of the arm. See note on this point in the translation of the passage by A. Platt, Oxford, 1910.

The reproductive processes of the Cephalopods were unknown to modern naturalists until the middle of the nineteenth century. Before that time several observers had noted the occasional presence of a peculiar parasite in the mantle cavity of female cephalopods and had described its supposed structure without tracing any relationship to the process of generation. In 1851 it was first shown that this supposed parasite was the arm of the male animal specially modified for reproductive purposes and broken off on insertion into the mantle cavity of the female. The actual process of reproduction does not seem to have been observed until 1894.

J. B. Verany, Mollusques méditerranéens, Genoa, 1851.

E. Racovitza. Archives de zoologie experimentale, Paris, 1894.

Aristotle is perhaps at his best and happiest when describing the habits of living animals that he has himself observed. Among his most pleasing accounts are those of the fishing-frog and torpedo. In these creatures he did not fail to notice the displacement of the fins associated with the depressed form of the body.

‘In marine creatures,’ he says, ‘one may observe many ingenious devices adapted to the circumstances of their lives. For the account commonly given of the frog-fish or angler is quite true; as is also that of the torpedo....

‘In the Torpedo and the Fishing-frog the breadth of the anterior part of the body is not so great as to render locomotion by fins impossible, but in consequence of it the upper pair [pectorals] are placed further back and the under pair [ventrals] are placed close to the head, while to compensate for this advancement they are reduced in size so as to be smaller than the upper ones.

‘In the Torpedo the two upper fins [pectorals] are placed in the tail, and the fish uses the broad expansion of its body to supply their place, each lateral half of its circumference serving the office of a fin.... The torpedo narcotizes the creatures that it wants to catch, overpowering them by the force of shock that is resident in its body, and feeds upon them; it also hides in the sand and mud, and catches all the creatures that swim in its way and come under its narcotizing influence. This phenomenon has been actually observed in operation.... The torpedo-fish is known to cause a numbness even in human beings.

‘The frog-fish has a set of filaments that project in front of its eyes; they are long and thin, like hairs, and are round at the tips; they lie on either side, and are used as baits.... The little creatures on which this fish feeds swim up to the filaments, taking them for bits of seaweed such as they feed upon. Accordingly, when the frog-fish stirs himself up a place where there is plenty of sand and mud and conceals himself therein, it raises the filaments, and when the little fish strike against them the frog-fish draws them in underneath into its mouth.... That the creatures get their living by this means is obvious from the fact that, whereas they are peculiarly inactive, they are often caught with mullets, the swiftest of fishes, in their interior. Furthermore, the frog-fish is usually thin when he is caught after losing the tips of his filaments.’

The paragraphs concerning the fishing-frog and torpedo are made up of sentences rearranged from the De partibus animalium, iv. 13; 696ᵅ 26, and the Historia animalium, ix. 37; 620ᵇ 15.

The modification of the musculature of the torpedo-fish for electric purposes and the fishing habits of the fishing-frog or Lophius are now well known, but it was many centuries before naturalists had confirmed the observations of the father of biology.

When we turn from Aristotle’s observations in the department of natural history to his discussion of the actual mechanism of the living body, the subject now contained under the heading Experimental Physiology, we are in the presence of much less satisfactory material. Aristotle here exhibits his weakness in physics and not being endowed with any experimental knowledge of that subject his physiological development is very greatly handicapped. He seems often to accept fancies of his own in place of generalizations from collated observations. This tendency of his was conveyed to his successors and delayed physiological advance for many centuries. It forms a striking contrast to the method of certain of the Hippocratic works such as the Epidemics and the Aphorisms which exhibit an investigator intent on recording actual observations and on deducing general laws therefrom. Had the Hippocratic method been extended by Aristotle beyond the field of natural history, where he freely follows it, to that of physiology, the succeeding generations might have established medicine far more firmly as a science.

An important factor in Aristotle’s physical and physiological teaching is the doctrine that matter is continuous and not made up of indivisible parts. He thus rejected the atomic views of his predecessors Leucippus and Democritus which have been preserved for us by the poem of Lucretius. The different kinds of matter existing merely in their state of simple mixture formed various uniform or homogeneous substances, homoeomeria, of which the tissues of living bodies provided one type. We now consider tissues as having structure made up of living cells or their products, but to Aristotle their structure was an essential fact following on their particular elemental constitution. The structure of muscle or flesh was perhaps comparable to that of a crystalline substance, for, as we have seen, Aristotle made no fundamental distinction between organic and inorganic substances, which are in his view alike subject to the processes of generation and corruption. The difference between them lies not in their structure but in their potential relation to the various degrees of soul, the vegetative, the animal, and the rational.

‘There are’, says Aristotle, ‘three degrees of composition, and of these the first in order is composition out of what some call the elements, earth, air, water, and fire....

‘The second degree of composition is that by which the homogeneous parts of animals (ὁμοιομερῆ), such as bone, flesh, and the like, are constituted out of [these] primary substances.

‘The third and last stage is the composition which forms the heterogeneous parts (ἀνομοιομερῆ) such as face, hand, and the rest.’

De partibus animalium, ii. 1; 646ᵅ 12.

The distinctions are not altogether clear but may perhaps be explained along such lines as the following. The division into homogeneous and heterogeneous corresponds in a general way to the later division into Tissues and Organs, the former, however, including much that we should not call tissue. The homogeneous parts were again of two kinds: (a) simple tissues or stuffs without any notion of size or shape, that is, mere substance capable of endowment with life or soul, e.g. cartilaginous or osseous tissues; and (b) simple structure, that is actual structure made of such a single tissue but with definite form and size, matter to which form had been added and which either was actually or had been endowed with soul, e.g. a cartilage or a bone.

As a physiologist Aristotle is, in fact, in much the same position as he is as a physicist. He never dissected the human body, he had only the roughest idea of the course of the vessels, and his description of the vascular system is so difficult and confused that a considerable literature has been written on its interpretation. He regarded the heart as the central organ of the body and the seat of sensation and he probably believed that the arteries contained air as well as blood. He made no adequate distinction between veins and arteries. He tells us that two great vessels arise from the heart and that the heart is, as it were, a part of these vessels. The two vessels are apparently the aorta and the vena cava, and a very elementary and not very accurate description is given of the branches of these vessels. He believed that the heart had three chambers or cavities and that it took in air direct from the lung.

The brain was for him mainly an organ by which were secreted certain cold humours which prevented any overheating of the body by the furnace of the heart under the action of the bellows of the lung. He formally rejected the older views of Diogenes of Apollonia, of Alcmaeon of Croton, and of the Hippocratic writings, that placed the seat of sensation in the brain. He failed to trace any adequate relation of sense organs and nerves to brain. He considered that the spinal marrow served to hold the vertebrae together.

De partibus animalium, ii. 10.