NATURAL SELECTION 83 



cat, according to Mr. St. John, bringing home cringed 

 game, another hares or rabbits, and another hunting on 

 marshy ground and almost nightly catching woodcocks 

 or snipes. The tendency to catch rats rather than 

 mice is known to be inherited. Now, if any slight 

 innate change of habit or of structure benefited an 

 individual wolf, it would have the best chance of 

 surviving and of leaving offspring. Some of its young 

 would probably inherit the same habits or structure, 

 and by the repetition of this process, a new variety might 

 be formed which would either supplant or coexist with 

 the parent form of wolf. Or, again, the wolves in- 

 habiting a mountainous district, and those frequenting 

 the lowlands, would naturally be forced to hunt different 

 prey ; and from the continued preservation of the 

 individuals best fitted for the two sites, two varieties 

 might slowly be formed. These varieties would cross 

 and blend where they met ; but to this subject of 

 intercrossing we shall soon have to return. I may add, 

 that, according to Mr. Pierce, there are two varieties 

 of the wolf inhabiting the Catskill Mountains in the 

 United States, one with a light greyhound-like form, 

 which pursues deer, and the other more bulky, with 

 shorter legs, which more frequently attacks the 

 shepherd's flocks. 



Let us now take a more complex case. Certain 

 plants excrete a sweet juice, apparently for the sake of 

 eliminating something inj urious from their sap : this is 

 effected by glands at the base of the stipules in some 

 Leguminos*, and at the back of the leaf of the common 

 laurel. This juice, though small in quantity, is 

 greedily sought by insects. Let us now suppose a 

 little sweet juice or nectar to be excreted by the inner 

 bases of the petals of a flower. In this case insects in 

 seeking the nectar would get dusted with pollen, and 

 would certainly often transport the pollen from one 

 flower to the stigma of another flower. The flowers of 

 two distinct individuals of the same species would thus 

 get crossed ; and the act of crossing, we have good 

 reason to believe (as will hereafter be more frilly 



