22 If, then, these things are vain, and are not supported by any reason, the very offering of sacrifices also is idle. For how can that which follows have a suitable cause, when that very first statement from which the second flows is found to be utterly idle and vain, and established on no solid basis? To mother Earth, they say, is sacrificed a teeming and pregnant sow; but to the virgin Minerva is slain a virgin calf, never forced by the goad to attempt any labour.
But yet we think that neither should a virgin have been sacrificed to a virgin, that the virginity might not be violated in the brute, for which the goddess is especially esteemed; nor should gravid and pregnant victims have been sacrificed to the Earth from respect for its fruitfulness, which we all desire and wish to go on always in irrepressible fertility. For if because the Tritonian goddess is a virgin it is therefore fitting that virgin victims be sacrificed to her, and if because the Earth is a mother she is in like manner to be entertained with gravid swine, then also Apollo should be honoured by the sacrifice of musicians because he is a musician; Aesculapius, because he is a physician, by the sacrifice of physicians; and because he is an artificer, Vulcan by the sacrifice of artificers; and because Mercury is eloquent, sacrifice should be made to him with the eloquent and most fluent.
Bat if it is madness to say this, or, to speak with moderation, nonsense, that shows much greater madness to slaughter pregnant swine to the Earth because she is even more prolific; pure and virgin heifers to Minerva because she is pure, of unviolated virginity.
Source: Against the Heathen (New Advent)