[In the following essay, Lloyd surveys the sources and types of empirical data Aristotle used in developing his biological treatises. Lloyd notes that while Aristotle does not always adhere to his methodology, he at least states his methodological principles. In conclusion, Lloyd emphasizes that despite the limitations of Aristotle's work, one should not undervalue the vast scope of his achievements in the area of biological inquiry.]

The range of Aristotle's investigations in zoology is such that a discussion of his use of empirical methods has to be drastically selective. Yet the need to come to some assessment of his performance in this field is all the more pressing in that it has been subject to such divergent judgments. Some of the most extravagant praise, but also some of the most damning criticisms, have been directed at his empirical researches in zoology.¹

The massive array of information set out in the main zoological treatises² can hardly fail to impress at the very least as a formidable piece of organization. But both Aristotle's sources and his principles of selection raise problems. As we have already noted in connection with his use of dissection, it is often impossible to distinguish Aristotle's personal investigations from those of his assistants, although, given the collaborative nature of the work of the Lyceum, that point is not a fundamental one. It is abundantly clear from repeated references in the text that he and his helpers consulted hunters, fishermen, horse-rearers, pig-breeders, beekeepers, eel-breeders, doctors, veterinary surgeons, midwives and many others with specialized knowledge of animals.³ But a second major source of information is what he has read, ranging from Homer and other poets, through Ctesias and Herodotus to many of the Hippocratic authors.⁴ In general he is cautious in his evaluations of all this secondary evidence. He points out, for example, that hunters and fishermen do not observe animals from motives of research and that this should be borne in mind.⁵ He recognizes, too, the need for experience—a trained eye will spot things that a layman will miss⁶—though even experts make mistakes.⁷ He frequently expresses doubts about the reports he has received, emphasizing that some stories have yet to be verified,⁸ or flatly rejecting them as fictions⁹—though understandably there are tall stories that he fails to identify as such¹⁰—and on some occasions the different degrees of acceptance exhibited in different texts may suggest some vacillation on his part.¹¹ He is particularly critical of some of his literary sources, describing Ctesias as untrustworthy¹² and Herodotus as a 'mythologist'.¹³ Yet he sometimes records baldly as 'what has been seen' something for which his principal or even his only evidence may be literary. Thus when at HA [History of Animals or, Historia Animalium] III. 516al9-20 we read that an instance 'has been seen' of a man's skull with no suture, his (unacknowledged) source may be the famous description of such a case on the battlefield of Plataea in Herodotus (IX 83). When we are told that lions are found in Europe only in the strip of land between the rivers Achelous and Nessus¹⁴ the authority for this may again be a passage in Herodotus (VII 126) which makes a similar suggestion, though the river Nessus appears by its alternative name Nestus.

Aristotle's use of these sources and of his own personal researches is, naturally, guided throughout by his theoretical interests and preoccupations. The very thoroughness with which he tackles the task of the description of animals reflects his declared aim to assemble the 'appearances' (phainomena), the differentiae of animals and their properties, before proceeding to state their causes.¹⁵ As we have noted, this very program obliges Aristotle to be comprehensive in his account, and certain features of the way he implements it stand out. His stated preference for the formal and final causes, rather than the material, dictates greater attention being paid to the functions of the organic and inorganic parts than to their material composition, although the latter is also discussed, indeed sometimes, as in the case of blood,¹⁶ at some length. More importantly, the form of the living creature is its psuche life or soul, and his psychological doctrines influence his investigations not only in insuring a detailed discussion of, for example, the presence or absence of particular senses in different species of animals in the De Sensu, of the different modes of locomotion in the De Motu and De Incessu, and of the fundamental problem of reproduction in the De Generatione Animalium, [GA] but also by providing the general framework for his description of the internal and external parts of animals in the Historia.

Thus at PA [Parts of Animals] 11.655b29ff. and Juv. 468a13ff. he identifies the three main essential parts of animals as (1) that by which food is taken in, (2) that by which residues are discharged, and (3) what is intermediate between them—where the arche or controlling principle is located: in addition animals capable of locomotion also have organs for that purpose, and in the corresponding passage in HA 1.2 and 3 he further adds reproductive organs where male and female are distinguished.¹⁷ In his detailed account of the internal and external parts of the four main groups of bloodless animals (cephalopods, crustacea, testacea and insects) in HA IV. 1-7 he evidently works quite closely to this broad and simple schema. Thus he regularly considers such questions as the position of the mouth, the presence or absence of teeth and tongue or analogous organs, the position and nature of the stomach and gut and of the vent for residue, as also the reproductive organs and differences between males and females. A series of passages shows that he actively considered whether or not certain lower groups produced residue and attempted to identify and trace the excretory vent.¹⁸ But while the whole course of the alimentary canal is thoroughly discussed in connection with each of the bloodless groups,¹⁹ he has little or nothing to say about the brain²⁰ or about the respiratory (or as he would say refrigeratory) system.²¹ Again while the external organs of locomotion are carefully identified and classified, the internal musculature is ignored throughout.²² It would certainly be excessive to suggest that his observations are everywhere determined by his preconceived schema: yet the influence that that schema exercised on his discussion is manifest.

In other cases too it is not hard to trace the influence of his theoretical preoccupations and preconceptions on his observational work, not only—naturally enough—on the questions he asked, but also—more seriously—on the answers he gave, that is on what he represents as the results of his research. His search for final causes is an often cited example though it is not so much his general assumption of function and finality in biological organisms as some of his rather crude particular suggestions, that are open to criticism: moreover he is clear that not everything in the animal serves a purpose²³ and that it is not only the final cause that needs to be considered. But many slipshod or plainly mistaken observations (or what purport to be such) relate to cases where we can detect certain underlying value judgments at work. The assumption of the superiority of right to left is one example that has been mentioned before.²⁴ His repeated references to the differences between man and other animals, and between males and females, are two other areas where errors and hasty generalizations are especially frequent. Man is not only marked out from the other animals by being erect—by having his parts, as Aristotle puts it, in their natural positions²⁵—and by possessing the largest brain for his size, hands and a tongue adapted for speech:²⁶ Aristotle also claims, more doubtfully, that man's blood is the finest and purest,²⁷ that his flesh is softest,²⁸ and that the male human emits more seed, and the female more menses, in proportion to their size.²⁹

While his general distinction between male and female animals relates to a capacity or incapacity to concoct the blood,³⁰ he records largely or totally imaginary differences in the sutures of the skull,³¹ in the number of teeth,³² in the size of the brain,³³ and in the temperature,³⁴ of men and women. His view that in general males are better equipped with offensive and defensive weapons than females³⁵ is one factor that leads him to the conclusion that the worker bees are male.³⁶ To be sure, he sometimes notes exceptions to his general rules, as when he remarks that although males are usually bigger and stronger than females in the non-oviparous blooded animals the reverse is true in most oviparous quadrupeds, fish and insects,³⁷ and while he goes along with the common belief that male embryos usually move first on the right-hand side of the womb, females on the left, he remarks that this is not an exact statement since there are many exceptions.³⁸ But although there are certainly inaccuracies in his reported observations besides those that occur where an a priori assumption is at work, those where that is the case form a considerable group.³⁹

We can document the influence of his over-arching theories on what he reports he has seen: but there are other occasions when the theories themselves appear to depend on, and may in some cases even be derived from, one or more observations (however accurate or inaccurate) which accordingly take on a particular significance for his argument. Undoubtedly the most striking example of this⁴⁰ is his often repeated statement that the heart is the first part of the embryo to develop. This is introduced at Fuv. 468b28ff. as something that is 'clear from what we have observed in those cases where it is possible to see them as they come to be'. At PA III. 666A18ff. he says that the primacy of the heart is clear not only according to argument, but also according to perception,⁴¹ and in reporting his investigation of the growth of hen's eggs in particular he remarks that after about three days the heart first appears as a blood spot that 'palpitates and moves as though endowed with life'.⁴² The circumstantial detail of this and other accounts show that they are based on first-hand inspection, although the conclusion Aristotle arrived at is not entirely correct: as Ogle put it, 'the heart is not actually the first structure that appears in the embryo, but it is the first part to enter actively into its functions'.⁴³ However the consequences of Aristotle's observation were momentous. This provides the crucial empirical support for his doctrine that it is the heart—rather than say the brain—that is the principle of life, the seat not just of the nutritive soul, but also of the faculty of locomotion and of the common sensorium. As in the physical treatises, so too in his biology, Aristotle often constructs a general theory largely by extrapolation from a slight—and sometimes insufficiently secure—empirical foundation.

Destructively, however, his deployment of observations to refute opposing theories is often highly effective. This can be illustrated first with some fairly straightforward examples. (1) The idea that drink passes to the lungs is one that we know to have been widely held,⁴⁴ although it is attacked by the author of the Hippocratic treatise On Diseases IV.⁴⁵ At PA III. 664b6ff. Aristotle dismisses it primarily on the simple anatomical grounds that there is no communicating link between the lungs and the stomach (as there is between the stomach and the mouth, namely the esophagus), and the confidence with which he rebuts the theory is clearly seen in his concluding remarks: 'but it is perhaps silly to be excessively particular in examining silly statements'.⁴⁶ (2) At GA II. 746a19ff. he refutes the view that human embryos are nourished in the womb by sucking a piece of flesh: if that were true, the same would happen in other animals, but it does not, as is easy to observe by means of dissection. And while that remark is quite general,⁴⁷ he follows it with a specific reference to the membranes separating the embryo from the uterus itself.⁴⁸ Dissection again provides the evidence to refute (3) those who held that the sex of the embryo is determined by the side of the womb it is on,⁴⁹ and (4) the view that some birds copulate through their mouths.⁵⁰

In such instances an appeal to easily verifiable points of anatomy was enough to undermine the theory. But more often no such direct refutation was possible, and Aristotle deploys a combination of empirical and dialectical arguments to attack his opponents' positions. One final example of this is his extended discussion, in GA I. 17 and 18, of the doctrine that later came to be known as pangenesis, that is the view that the seed is drawn from the whole of the body.⁵¹ Here most of what passed as empirical evidence was agreed on both sides, and the strengths of Aristotle's discussion lie in his acute exploration first of the coherence of his opponents' doctrine, and secondly of the inferences that could legitimately be drawn from the available data.

One of the principal arguments he mounts against pangenesis poses a dilemma:⁵² the seed must be drawn either (1) from all the uniform parts (such as flesh, bone, sinew) or (2) from all the non-uniform parts (such as hand, face) or (3) from both. Against (1) he objects that the resemblances that children bear to their parents lie rather in such features as their faces and hands, than in their flesh and bones as such. But if the resemblances in the non-uniform parts are not due to the seed being drawn from them, why must the resemblances in the uniform parts be explained in that way? Against (2) he points out that the non-uniform parts are composed of the uniform ones: a hand consists of flesh, bone, blood and so on. Moreover this option would suggest that the seed is not drawn from all the parts. He tackles (3) too by considering what must be said about the non-uniform parts. Resemblances in these must be due either to the material—but that is simply the uniform parts—or to the way in which the material is arranged or combined. But on that view, nothing can be said to be drawn from the arrangements to the seed, since the arrangement is not itself a material factor. Indeed a similar argument can be applied to the uniform parts themselves, since they consist of the simple bodies combined in a particular way. Yet the resemblance in the parts is due to their arrangement or combination, and has therefore to be explained in terms of what brings this about,⁵³ and not by the seed being drawn from the whole body.

A series of further arguments follow, for example that the seed cannot be drawn from the reproductive organs at least, because the offspring has only male or female organs, not both (GA I. 722b3ff.), and again that the seed cannot be drawn from all the parts of both parents, for then we should have two animals (b6ff.). At GA I. 722b3off. he considers how the uniform and non-uniform parts are to be defined, namely in terms of certain qualities and functions respectively. Thus unless a substance has certain qualities it cannot be called 'flesh'. But it is plain that we cannot call what comes from the parent flesh, and we must agree that that comes from something which is not flesh.⁵⁴ But there is no reason not to agree that other substances may do the same, so again the idea that all the substances in the body are represented in the seed fails.

At the same time it is notable that he not only challenges the scope and significance of the evidence his opponents cite, but also shows some ingenuity in collecting other data that pose difficulties for them. One of the main arguments they used depended on the supposed fact that mutilated parents produce mutilated offspring, and among the evidences (marturia) they cited was that of children born with scars where their parents were scarred, and a case at Chalcedon of a child of a branded father born with a faint brand mark: it was claimed, as Aristotle puts it, that children resemble their parents in respect not only of congenital characteristics (ta sumphuta) but also of acquired ones (ta epikt ta).⁵⁵ But this he counters simply by pointing out that not all the offspring of mutilated parents are themselves mutilated, just as not all children resemble their parents.⁵⁶ Among the evidence he brings against pangenesis he cites (1) that many plants lack certain parts (they can be torn off, and yet the seed thereafter produces a new plant that is identical with the old, GA I. 722allff.) and (2) that plant cuttings bear seed—from which he says it is clear that even when the cutting belonged to the original plant the seed it bore did not come from the whole of that plant (GA I. 723b16ff.).

But the most important consideration, in his view, is (3) what he claims to have observed in insects (GA I. 723b 19ff.). In most cases, during copulation the female insect inserts a part into the male, rather than the male into the female. This by itself looks quite inconclusive, but Aristotle believes that in such cases it is not semen, but simply the heat and the dunamis (capacity) of the male that brings about generation by 'concocting' the fetation.⁵⁷ He remarks quite cautiously that not enough observations have been carried out in such cases to enable him to classify them by kinds, and his remark that the males do not have seminal passages is introduced with phainetai in the tentative sense, 'appears' rather than 'it is evident'.⁵⁸ Yet this erroneous observation is not only his 'strongest evidence'⁵⁹ against pangenesis, but also one of the crucial pieces of 'factual' support that he cites for his own view that the role of the male in reproduction is to supply the efficient cause, not to contribute directly to the material of the offspring.⁶⁰ In the main the arguments mounted against pangenesis are telling ones, and they draw on well known, and some not so well known, data to good effect: even so, the chief point that derives from Aristotle's personal researches in these chapters is one where, under the influence, no doubt, of his general theories, he assumed too readily that his observations yielded a conclusion that supported them.

It is apparent that much of Aristotle's biology—like his physics—does not live up to his own high ideals. His drawing attention to the inadequacy of certain of the information available to him and to the need to survey all the relevant huparchonta ('data'),⁶¹ does not prevent him from being less than persistent in his research in some areas, nor deter him from some highly speculative theories in others. Where he remarks on other writers' inexperience of internal anatomy, for example,⁶² or charges them with not taking what is familiar as the starting-point of their inquiries,⁶³ with generalizing from a few cases or otherwise jumping to conclusions on inadequate evidence,⁶⁴ or with guessing what the result of a test would be and assuming what would happen before actually seeing it,⁶⁵ in each case similar criticisms could be leveled at him to some—if not the same—extent.

Nevertheless two simple but fundamental points remain. First, if he does not always live up to his own methodological principles, at least they are stated as the principles to follow. The end is defined in terms of giving the causes and resolving the difficulties in the common assumptions: he is no fact-collector for the sake of fact-collecting. But as means to his ends the appeal to the evidence of the senses is allotted its distinct role, alongside the reference to generally accepted opinions and the use of reasoned argument, and he makes it clear that in certain contexts at least it is the first of these that is to be preferred. Moreover his is the first generalized program of inquiry into natural science: his doctrine of causes identifies the kind of questions to be asked, and he provides an explicit protreptic to the study of each branch of natural science as far as each is possible.⁶⁶

Secondly the limitations of his observational work should not lead us to ignore the extrordinary scope of what he did achieve in the various departments of the inquiry concerning nature. An analysis of what he says he has observed and of how he uses this to support his theories sometimes reveals the superficiality of his empirical research. Yet as the first systematic study of animals, the zoological treatises represent a formidable achievement, not only in the individual discoveries that are recorded, but also in the patient and painstaking amassing of a vast amount of data concerning many different species and in the ingenious interplay of data and arguments in his assault on such obscure problems as those connected with reproduction.

Notes

This selection is excerpted from Lloyd 1979: ch. 3, 'The development of empirical research', pp. 211-20.

¹ Contrast the evaluations in, for example, Bourgey 1955 and Lewes 1864.

² The authenticity of some of the later books of HA (VII, VIII and IX) is open to doubt, but I shall treat the whole (with the exception of X, which most scholars treat as un-Aristotelian) as evidence for work organized and planned by Aristotle, if not carried out by him. Recently D. M. Balme has argued for the authenticity of I-IX, as a whole (Introduction to Balme forth-coming, and ch. I above, 16-17) and, as an earlier work not part of HA, of X (Balme 1985).

³ There is a convenient analysis of Aristotle's principal sources in Manquat 1932: 31ff., 49ff., 59ff. Cf. also Lones 1912, Le Blond 1939:223ff., Bourgey 1955:73ff., 83ff., Louis 1964-9:xxxiv ff., Preus 1975:21ff., Byl 1980.

⁴ See Manquat 1932: chs. 4 and 5, and cf. the analyses of the relationship between Aristotle and the Hippocratic treatises in Poschenrieder 1887 and Byl 1980.

⁵ See, e.g., GA III. 756a33.

⁶ See, e.g., HA VI. 566a6-8 (outside the breeding season, the sperm-ducts of cartilaginous fish are not obvious to the inexperienced), 573allff., 574b15ff.

⁷ E.g. GA III. 756b3ff.

⁸ E.g. HA I. 493b14ff., VI. 580al9-22. That further research is necessary is a point repeatedly made in other contexts as well.

⁹ E.g. HA VI. 579b2ff., VIII. 579a32ff. PA III. 673alO-31 is a careful discussion of stories about men laughing when wounded in the midriff: he rejects as impossible the idea that a head, severed from the body, could speak (since voice depends on the windpipe) but accepts that movement of the trunk may occur after decapitation.

¹⁰ E.g. HA V. 552b 15ff. on the salamander extinguishing fire.

¹¹ As in the notable case of his reports on the phenomenon now known as the hectocotylization of one of the tentacles of the octopus, recorded without endorsement at HA V. 541b8ff., cf. 544a12ff., and apparently accepted at IV. 524a5ff., but rejected at GA I. 720b32ff. Such divergences may, of course, indicate not a change of mind, but inauthentic material in, or plural authorship of, the zoological works.

¹²HA IX. 606a8.

¹³ The context suggests that the term muthologos, used of Herodotus at GA III. 756b6ff., there carries pejorative undertones.

¹⁴HA VI. 579b5ff., cf. VIII. 606b14ff.

¹⁵ See PA I. 639b8ff., 640al4-15, HA I. 491a9ff. especially.

¹⁶ E.g. PA 11.4 and cf. the subsequent chapters on fat, marrow, brain, flesh and bone. PA 11.2 discusses the problems posed by the ambiguity of hot and cold and stresses the difficulty of determining which substances are hot and which cold.

¹⁷HA I. 488b29ff., especially 489a8ff., and cf. also PA II. 650a2ff.

¹⁸ See HA IV. 530a2ff., 531a12ff., b8ff.

¹⁹HA IV. 527b1ff. concludes that the stomach, esophagus and gut alone are common to bloodless and blooded groups (the passage is considered suspect by some editors, but it sums up Aristotle's position well enough). In the strictest sense in which the term splanchnon is reserved for red-blooded organs, the bloodless animals have no viscera at all, but only what is analogous to them: HA IV. 532b7ff., PA III. 665a28ff., IV. 678a26ff.

²⁰ In HA IV. 1-7 the brain is mentioned only at 524b4 and in a probably corrupt passage, 524b32. Cf. HA I. 494b27ff., and PA II. 652b23ff.

²¹ In Resp. 475b7ff., however, he says that the crustacea and octopuses need little refrigeration and at 476b30ff. that the cephalopods and crustacea effect this by admitting water, which the crustacea expel through certain opercula, that is the gills (cf. also HA IV. 524b21ff.).

²² This point can be extended also to his descriptions of the blooded animals. Although his account of the external organs of locomotion in IA is, on the whole, quite detailed, he has almost nothing to say of the disposition and functioning of the muscles. Similarly his osteology (with the exception of his description of the limbs) is in general crude: even though he writes in praise of the hand, remarking on the importance of the opposition of thumb and fingers for prehension (see PA IV. 687a7ff., b2ff., 690a30ff.) he limits his account of its bones to remarks on the number of fingers and toes in the forelimbs of different species.

²³ There is an explicit statement to this effect at PA IV. 677a l5 ff., for example.

²⁴ The main examples of anatomical doctrines influenced by his beliefs that right is superior to left, up to down, and front to back, are collected in Lloyd 1973.

²⁵ E.g. PA II. 656alOff., IA 706al9-20, b9-10.

²⁶ See, e.g., PA II. 653a27ff., IV. 687b2ff., II. 660a17ff. and Lloyd 1983: 26ff.

²⁷ See HA III. 521a2ff., cf. PA II. 648a9ff., Resp. 477a20-1.

²⁸PA II. 660all, cf. GA V. 781b21-2.

²⁹ See HA III. 521a26-7, HA VII. 582b28ff., 583a4ff., GA I. 728b 14ff.

³⁰ See GA I. 728a18ff., IV. 765b8ff. and Lloyd 1983: 94ff.

³¹ See HA 1. 491b2ff., HA III. 516a18ff., PA II. 653bl.

³² See HA II. 501b19ff.

³³ See PA II. 653a28ff. (on which see Ogle 1882: 167).

³⁴ E.g. GA IV. 765b16-17, 775a5ff.

³⁵ E.g. HA IV. 538b15ff., PA III. 661b28ff.

³⁶ See GA III. 759b2ff.

³⁷HA IV. 538a22ff., V. 540b15-16, GA I. 721a17ff.

³⁸ See HA VII. 583b2ff., and 5ff., and cf. further below, p. 59, on GA IV. 764a33ff. Cf. also HA VII. 584a12ff. on exceptions to the rule that women have easier pregnancies with male children.

³⁹ Another important group of mistakes relates to exotic species (for which parts of HA especially show some predilection) where he was, no doubt, relying more on secondary sources or hearsay. Thus many of his statements about the lion are erroneous (see Ogle 1882:236). See also the mistakes mentioned by Bourgey 1955:84-5 (there are inaccuracies in those listed by Lewes 1864:164ff.).

⁴⁰ Two others would be (1) his claim to have verified that the brain is cold to touch, PA II. 652a34-5 (not true of a recently dead warm-blooded animal)—which was no doubt a major factor in contributing to his theory that the primary function of the brain is to counterbalance the heat of the heart and (2) his reported observation that a bull that had just been castrated was able to impregnate a cow (GA I. 717b3ff., cf. HA III. 510b2ff.)—which presumably influenced his doctrine that the testes are mere appendages, not integral to the seminal passages (e.g. GA I. 717a34ff.).

⁴¹ Again at GA II. 740a3ff. he says that not only perception but also argument shows that the heart is the first part to become distinct in actuality. Cf. also PA III. 666a8ff., GA II. 740al7-18, 741bl5-16.

⁴²HA VI. 561a6ff., 11-12, PA III. 665a33ff.

⁴³ Ogle 1897: 110 n. 24, and cf. 1882: 193.

⁴⁴ This we know from Morb. IV ch. 56, Littre VII 608.17ff. The view is found in Plato, Ti. 70c, is attributed to Philistion by Plutarch (Quaest. Conv. VII I, 698A ff., at 699C) and after Aristotle was the subject of an attempted experimental demonstration in Cord. ch. 2, Littre IX 80.9ff.

⁴⁵ The nine proofs, historia, that this author adduces are a very mixed bag: they include not only a reference to the epiglottis and its function (VII 608.23ff.) but also arguments that if drink went to the lungs, one would not be able to breathe or speak when full, that another consequence would be that dry food would not be so easily digested, that eating garlic makes the urine smell, and other often inconclusive or question-begging considerations, see VII 606.7ff.

⁴⁶PA III. 664b18-19.

⁴⁷ Some of Aristotle's general appeals to what would be shown by dissection are clearly hypothetical and were not followed up: thus at PA IV. 677a5ff. he dismisses the view of Anaxagoras' followers that the gallbladder causes acute diseases with the claim that those who suffer from such diseases mostly have no gallbladder and 'this would be clear if they were dissected'.

⁴⁸GA II. 746a23ff. says that this is true for all embryos in animals that fly, swim and walk.

⁴⁹GA IV. 764a33ff., cf. 765a16ff.; yet he is prepared to allow that males often move first on the right-hand side (HA VII. 583b2ff.; cf. b5ff.), and also that, given that the right-hand side of the body is hotter than the left, and that hotter semen is more concocted, seed from the right side is more likely to produce males (GA IV. 765a34ff., but cf. b4ff.).

⁵⁰GA III. 756b16ff., especially 27ff.

⁵¹ Our principal original sources for the pangenesis doctrine are the Hippocratic treatises, Genit., Nat. Puer. and Morb. IV. See Lesky 1951: 70ff and Lonie 1981.

⁵²GA I. 722al6-b3.

⁵³ The semen has just such a function, as supplying the efficient cause, in Aristotle's own theory.

⁵⁴ He is led from this to consider Anaxagoras' theory that none of the uniform substances comes into being.

⁵⁵GA I. 721b17ff., and 28ff.

⁵⁶GA I. 724a3ff., cf. HA VII. 585b35ff.

⁵⁷ See especially GA I. 729b21-33, and cf. other references to species that do not emit seed in copulation, 731a14ff., II. 733b16ff.

⁵⁸ See GA I. 721al2, 14ff.

⁵⁹GA I. 723bl9.

⁶⁰ See GA I. 729b8-9 and 21-2, where in both cases there is a contrast between logos and erga. Cf. also b33ff. with some equally doubtful evidence such as the supposed fact that a hen bird trodden twice will have eggs that resemble the second cock.

⁶¹ Apart from PA I. 639b8ff., 640a14ff., HA I. 491a9ff., see also, e.g., GA II. 735b7-8, 748a14ff.

⁶² See, e.g., Resp. 470b8-9, 471b23ff.

⁶³ E.g. GA II. 747b5-6, 748a8-9, IV. 765b4-5.

⁶⁴ E.g. PA IV. 676b33ff., GA III. 756a2ff., b16ff., V. 788b 1 Iff., 17ff.

⁶⁵GA IV. 765a25-9.

⁶⁶PA 1.5 644b22ff.: the study of the heavenly bodies and of animals each has its own attractions.