Home was an anatomist, not a taxonomist, and therefore he did not bother overmuch about classifying, limiting himself to describing what he saw. But the analogy with the reproductive organs of BIRDS and REPTILES could hardly fail to make him think the platypus was OVIPAROUS, or perhaps merely oviparous (as we now know, it is oviparous, but it is not OVIPAROUS), and he decided that it might be ovi-viviparous: the eggs were formed inside the mother’s body but then dissolved. Home found a supporter for his hypothesis in the anatomist Richard Owen, but by 1819 he was inclined toward viviparity (and this hypothesis usually crops up every time people reflect on the paradox of a furry animal born from an egg).
Home also found that the platypus resembled the echidna, already described by Shaw in 1792. But two similar animals ought to refer back to a common genus, and he guessed it might be that of Ornithorhynchus hystrix. Apart from that he expatiated at some length on the spur on the hind foot of the male, on the smooth beak and the rest of the body covered with fur, on the wrinkly tongue that served in lieu of teeth, on the penis suited for the passage of sperm, on the external orifice of the penis subdivided into various apertures, so that the sperm might be spread over a wide area, et cetera. At the end he spoke of a “tribe” that was certainly related to BIRDS and AMPHIBIANS, thereby putting forward, before Darwin, an idea very close to that of the evolutionary relation.
4.5.2 Mammae Without Nipples
In 1803, the protoevolutionist Etienne Geoffroy de Saint-Hilaire created the category of the MONOTREMES (and here too the term expresses a property: “with a single orifice”). He did not know yet where to put these animals, but assumed they were oviparous. Six years later, Lamarck created a new class, the PROTOTHERIA, saying they were not MAMMALS, because they had no mammary glands, and were probably oviparous; they were not birds, because they had no wings, and they were not reptiles, because they had a heart with four chambers.14 If a class were to define an essence, we would have here two fine cases of pure nominalism. But at this point the need to categorize gave free play to the imagination of men of science: in 1811, Illiger was talking of REPTANTIA, intermediates between REPTILES and MAMMALS; in 1812, Blainville was talking of MAMMALS in the order of the ORNITHODELPHIA.
It is clear that it is the properties that decide whether the animal is assigned to one class or the other, and some people were already arguing that as a newborn creature with a beak cannot suckle milk, we ought to forget about MAMMALS. But the fact is that even a hypothesis about the class drives one to seek out or overlook some properties, or even to disregard them.
A case in point would be the business of the mammary glands, which were discovered in 1824 by the German anatomist Meckel. They are very large, practically covering the whole body from the front to the hind limbs, but they are visible only when the creature is nursing its young, after which their size is reduced, and this explains why they had not been previously identified.
Is an animal with mammae a MAMMAL? Yes, if it also has nipples, but the female platypus does not have these, not to mention the male. Instead it has porelike glands on the surface, rather like sweat glands that secrete milk. Today we know that this is how it is, and that the young take milk by licking, but Saint-Hilaire was not all wrong in refusing to see these organs as mammae, also because he was firmly convinced that the MONOTREMES were OVIPAROUS and could therefore not be MAMMALS. He considered the glands seen by Meckel as something like the glands on the flanks of the shrew, which secrete a substance for attracting a partner during the mating season. Perhaps they were glands that secreted a perfume, or a substance that made the fur waterproof, or something like the so-called mammary glands of seals and whales, which secrete not milk but a mucus that clots in the water and serves as food for their young.
But Owen, a supporter of the ovoviviparous hypothesis, suspended that secretion in alcohol and obtained something that seemed milk and not mucus. Saint-Hilaire did not give in. The reproductive apparatus was that of an OVIPAROUS animal; an OVIPAROUS animal can only produce an egg; an animal born from an egg is not breast-fed. In 1829, given that the MONOTREMES could not be MAMMALS; could not be birds, because they had neither wings nor feathers; could not be REPTILES, because they were warm-blooded; and, with their lungs sheathed in a pleura and separated from the abdomen by a diaphragm, could not even be FISH, Saint-Hilaire decided that it was necessary to invent for them a fifth category of VERTEBRATES (note that in those days AMPHIBIANS did not yet constitute a class in themselves and were normally classified among the REPTILES).
In doing this, Saint-Hilaire was appealing to a principle that strikes me as very important. Taxonomies, he said, are not just ways of ordering, they are guides to action. If we put the MONOTREMES among the MAMMALS, the question may be considered settled, while if we put them to one side, we are obliged to go in search of new properties. In a certain sense Saint-Hilaire was proposing the creation of an “open” genus, so as to avoid making a clumsy classification of the unknown object, a type that must stand as a stimulus to conjecture. And therefore he stubbornly waited for those eggs that had not yet been discovered but that sooner or later had to appear.
4.5.3 A la Recherche de l’oeuf Perdu
As we now know, Saint-Hilaire lost the battle of the mammae (and therefore the platypus was to be a MAMMAL, although it seems ill—at-ease sitting there all alone with only the echidna for company in the jump seat reserved for the monotremes), but he won the battle of the eggs.
As early as 1817, John Jameson had made mention of the eggs in a letter from Sydney. The datum was not certain, but in 1824 Saint-Hilaire took it as proven. It is not easy to see a platypus while it is laying eggs (one supposes it does so in private, in the depths of a burrow inaccessible to human explorers), and so one puts one’s trust in those who ought to know more about it, in natives. Patrick Hill wrote in 1882 that “Cookoogong, a native, chief of the Boorah-Boorah tribe, says that they all know that this animal lays two eggs, of the size, color and shape of hen’s eggs.” Today we know that the eggs are tiny, one third of an inch long: either Cookoogong was wrong about the size, or he expressed himself badly in English, or Hill did not understand his language. Nor can we exclude the possibility that the aborigine chief had lied in order to please the explorer.
In 1829, new information reached Saint-Hilaire: someone had seen some eggs, laid in a hole in the sand, this time shaped like the eggs of a bird, snake, or lizard. He also received a drawing, and therefore his informers might really have seen the eggs. Unfortunately it is now thought that these were probably the eggs of a turtle, Chelodina longicollis. But Saint-Hilaire maintained that eggs of that size could not pass through the birth canal of a female platypus—and he was right, but for the wrong reasons, because he did not take into account that the eggs found in the sand had probably been in an advanced phase of development.
In 1831, Lieutenant Maule opened some burrows and found eggshells. The opponents of oviparity said the shells were excrement covered with urinary salts such that occur in birds, seeing that both urine and feces are expelled through the same orifice. In 1834, Doctor George Bennet, a supporter of viviparity, led some native informers into making contradictions on the subject of the eggs: he drew an oval egg, and they told him it was a Mullagong egg, then he drew a round one, and they repeated that it was the cabango (egg) of the Mullagong.
However, they then said that the newborn animal “tumbled down.” You don’t tumble down out of an egg, but from the womb. Bennett admitted that the natives could not speak English well, but who knows what he asked them and what they understood, who knows what his ovals and circles were like. Better a Gavagai than a Mullagong.
In 1865, Richard Owen (of the anti-egg party) received a letter from a certain Nicholson sent in September 1864, which said how ten months previously a female had been captured and given to the district Gold-receiver. This person had put the animal in a cage, where on the following morning he found two eggs, this time about the size of a crow’s egg, soft and without a calcareous shell. Nicholson said he had seen them, but two days later someone threw them away and killed the animal (finding in the belly many of what
