To save his argument from this antagonism of the facts, Darwin resorts to the ingenious expedient of distinguishing between _rudimentary_ organs and _nascent_ organs. Rudimentary organs are undeveloped organs, which are wholly, or partially, useless. They have had a past, but have no future. Nascent organs, on the contrary, are undeveloped organs, which “are of high service to their possessors” (“Descent of Man,” ch. I, p. 28, 2nd ed.). They “are capable of further development” (_ibidem_), and have, therefore, a future before them. He gives the following examples of rudimentary organs: “Rudimentary organs ... are either quite useless, such as teeth which never cut through the gums, or almost useless, such as the wings of an ostrich, which serve merely as sails.” (“Origin of Species,” 6th ed., ch. XIV, p. 469.) As an example of a nascent organ, he gives the mammary glands of the oviparous Duckbill: “The mammary glands of the Ornithorhynchus may be considered, in comparison with the udders of a cow, as in a nascent condition.” (_Op. cit._, ch. XIV, p. 470.) Darwin admits that it is hard to apply this distinction in the concrete: “It is, however, often difficult to distinguish between rudimentary and nascent organs; for we can judge only by analogy whether a part is capable of further development, in which case alone it deserves to be called nascent.” (_Op. cit._, ch. XIV, p. 469.) For Darwin “judging by analogy” meant judging on the assumption that evolution has really taken place; for he describes rudimentary organs as being “of such slight service that we can hardly suppose that they were developed under the conditions which now exist.” (“Descent of Man,” ch. I, p. 29.) He is somewhat perplexed about applying this distinction to the penguin: “The wing of the penguin,” he admits, “is of high service, acting as a fin; it may, therefore, represent the nascent state: not that I believe this to be the case; it is more probably a reduced organ, modified for a new function.” (“Origin of Species,” 6th ed., ch. XIV, pp. 469, 470.) In other words, there is scarcely any objective consideration by which the validity of this distinction can be checked up in practice. Like homology and convergence, like palingenesis and cænogensis, the distinction between rudimentary and nascent organs is a convenient device, which can be arbitrarily manipulated according to the necessities of a preconceived theory. It is “scientific” sanction for the privilege of blowing hot and cold with the same breath.