{37} The importance of exposure to new conditions for several generations is insisted on in the _Origin_, Ed. i. p. 7, also p. 131. In the latter passage the author guards himself against the assumption that variations are "due to chance," and speaks of "our ignorance of the cause of each particular variation." These statements are not always remembered by his critics. {38} Cf. _Origin_, Ed. i. p. 10, vi. p. 9, "Young of the same litter, sometimes differ considerably from each other, though both the young and the parents, as Mueller has remarked, have apparently been exposed to exactly the same conditions of life." {39} This is paralleled by the conclusion in the _Origin_, Ed. i. p. 8, that "the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception." {40} The meaning seems to be that there must be some variability in the liver otherwise anatomists would not speak of the 'beau ideal' of that organ. [All such] variations [being congenital] or those very slowly acquired of all kinds [decidedly evince a tendency to become hereditary], when not so become simple variety, when it does a race. Each{41} parent transmits its peculiarities, therefore if varieties allowed freely to cross, except by the _chance_ of two characterized by same peculiarity happening to marry, such varieties will be constantly demolished{42}. All bisexual animals must cross, hermaphrodite plants do cross, it seems very possible that hermaphrodite animals do cross,--conclusion strengthened: ill effects of breeding in and in, good effects of crossing possibly analogous to good effects of change in condition <?>{43}. {41} The position of the following passage is uncertain. "If individuals of two widely different varieties be allowed to cross, a third race will be formed--a most fertile source of the variation in domesticated animals. <In the _Origin_, Ed. i. p. 20 the author says that "the possibility of making distinct races by crossing has been greatly exaggerated."> If freely allowed, the characters of pure parents will be lost, number of races thus <illegible> but differences <?> besides the <illegible>. But if varieties differing in very slight respects be allowed to cross, such small variation will be destroyed, at least to our senses,--a variation [clearly] just to be distinguished by long legs will have offspring not to be so distinguished. Free crossing great agent in producing uniformity in any breed. Introduce tendency to revert to parent form." {42} The swamping effect of intercrossing is referred to in the _Origin_, Ed. i. p. 103, vi. p. 126.