McArthur, riding his hobby enthusiastically, quite forgot the character of his listeners, and laid his theories regarding the interchange of mammalian life between America and Asia during the early Pleistocene period, before Meeteetse Ed, Old Man Rulison, Tubbs, and others, in the same language in which he would have argued moot questions with colleagues engaged in similar research. The language of learning was as natural to McArthur as the vernacular of the West was to Tubbs, and in moments of excitement he lapsed into it as a foreigner does into his native tongue under stress of feeling. "I maintain," asserted McArthur, with a gesture of emphasis, "that the Paleolithic man of Europe followed the mastodon to North America and here remained." Meeteetse Ed, whose cheeks were flushed, laid his hot hand upon his forehead and declared plaintively as he blinked at McArthur: "Pardner, I'm gittin' a headache from tryin' to see what you're talkin' about." "Air you sayin' anything a-tall," demanded Old Man Rulison, suspiciously, "or air you joshin'?" "Them's words all right," said Tubbs. "Onct I worked under a section boss over on the Great Northern what talked words like them. He believed we sprung up from tuds and lizards--and the likes o' that. Yes, he did--on the square." "There are many believers in the theory of evolution," observed McArthur. "That's it--that's the word. That's what he was." Then, in the tone of one who hands out a clincher, Tubbs demanded: "Look here, Doc, if that's so why ain't all these ponds and cricks around here a-hatchin' out children?" "Guess that'll hold him for a minute," Meeteetse Ed whispered to his neighbor. But instead of being covered with confusion by this seemingly unanswerable argument, McArthur gazed at Tubbs in genuine pity. "Let me consider how I can make it quite clear to you. Perhaps," he said thoughtfully, "I cannot do better than to give you Herbert Spencer's definition. Spencer defines evolution, as nearly as I can remember his exact words, as an integration of matter and concomita, dissipation of motion; during which the matter passes from an indefinite heterogeneity to a definite, incoherent heterogeneity, and during which the retained motion undergoes a parallel transformation. Materialistic, agnostic, and theistic evolution----" Meeteetse Ed fell off his chair in a mock faint and crashed to the floor. Susie, who had entered, saw McArthur's embarrassment, and refused to join in the shout of laughter, though her eyes danced. "Don't mind him," she said comfortingly, as she eyed Meeteetse, sprawled on his back with his eyes closed. "He's afraid he'll learn something. He used to be a sheep-herder, and I don't reckon he's got more'n two hundred and fifty words in his whole vocabulary. Why, I'll bet he never _heard_ a word of more'n three syllables before. Get up, Meeteetse. Go out in the fresh air and build yourself a couple of them sheep-herder's monuments. It'll make you feel better."