sect, x.] INTRODUCTION. 59 



occur in neighbouring lochs. None weighed more than h lb. Yarhell, 

 Brit. Fishes, I. p. 286, figure given. 



Another specimen (Fig. 6), agreeing closely with Yarrell's figure, 

 was taken in a lake at an altitude of over 6000 ft. in the valley of 

 Sept-Laux (Isere). Saving the head it was in all respects normal. 

 This specimen is described and figured by Carlet, M. G., Journ. 

 de VAnat. et Phys., 1879, xv. p. 154. [It is declared that the 

 fishermen who took it, having previously met with similar speci- 

 mens, supposed that they had found a new species, but it is not 

 expressly stated that these other specimens were from the same 

 locality.] 



Before ending this preliminary glance at Discontinuity in 

 Substantive Variation, allusion must be made to a case which is 

 at once more famous and more instructive than any other. I refer 

 to the celebrated phenomenon of the production of nectarines by 

 peaches, or conversely. Upon the subject of almond, peach and 

 nectarine, Darwin produced a body of facts which, whether as an 

 example of a method or for the value of the facts themselves, 

 form perhaps the most perfect and the most striking of all that he 

 gave. 



The evidence which is there collected is known to all, and 

 though similar observations have been made since by many, there 

 is I believe nothing of importance to add to Darwin's statement. 

 The bearing of these phenomena on the nature of Discontinuity in 

 Variation is so close that Darwin's summary may with profit be 

 given at length. 



\" To sum up the foregoing facts ; we have excellent evidence of 

 peach-stones producing nectarine-trees, and of nectarine-stones 

 producing peach-trees — of the same tree bearing peaches and 

 nectarines — of peach-trees suddenly producing by bud-variation 

 nectarines (such nectarines reproducing nectarines by seed), as 

 well as fruit in part nectarine and in part peach, — and, lastly, of 

 one nectarine-tree first bearing half-and-half fruit and subsequently 

 true peaches" 1 . After disposing of alternative hypotheses he 

 concludes that " we may confidently accept the common view- 

 that the nectarine is a variety of the peach, which may be pro- 

 duced either by bud-variation or from seed." 



In this case the evidence is complete. The variation from peach 

 to nectarine or from nectarine to peach may be total. If less than 

 total, the fruit may be divided into either halves or quarters"'', 

 so that for each segment the Variation is total still. Of inter- 

 mediate forms other than these divided ones, we have in this case 



1 Animals and Plants under Domestication, ed. 2, i. p. 362. 



2 Ibid., p. 362, quoting from Loudon's Gard. Mag. 1828, p. 53. The case of a 

 Royal George peach which produced a fruit, " three parts of it being peach and one 

 part nectarine, quite distinct in appearance as well as in flavour." The lines of 

 division were longitudinal. 



