476 L-\"WS Of MULTIPLICATION. 



We have here the solution of various minor anomalies bj 

 which the inverse variation of Individuation and Genesis is 

 obscured. Take as an instance the fertility of the Blackbird 

 as compared with that of the Linnet. Both birds lay five eggs, 

 and both usually have two broods. Yet the Blackbird is far 

 the larger of the two ; and ought, according to the general 

 law, to be much less prolific. What causes this noncon- 

 formity ? We shall find an ansvrer in their respective foods 

 and habits. Except during the time that it is rearing its 

 young, the Linnet collects only vegetal food — lives during 

 the winter on the seeds it finds in the fields, or, when hard 

 pressed, picks up around farms; and to obtain this spare 

 diet is continually flying about. The result, if it survives the 

 frost and snow, is a considerable depletion ; and it recovers 

 its condition only after some length of spring weather. The 

 Blackbird, on the other hand, is omnivorous : while it eats 

 grain and fruit when they come in its way, it depends largely 

 on animal food. It cuts to pieces and devours the dew- worms 

 which, morning and evening, it finds on the surface of a lawn, 

 and, even discovering where they are, unearths them ; it 

 swallows slugs, and breaking snail-shells, either with its beak 

 or by hammering them against stones, tears out their tenants; 

 and it eats beetles and larvse. Thus the strength of the 

 Blackbird opens to it a store of good food, much of which is 

 inaccessible to so small and weak a bird as a Linnet — a store 

 especially helpful to it during the cold months, when the 

 hybernating Snails in hedge-bottoms yield it abundant pro- 

 vision. The result is that the Blackbird is ready to breed 

 very earlj^ in spring ; and is able during the summer to rear 

 a second, and sometimes oven a third, brood. Here, then, a 

 higher degree of Individuation secures advantages so great, 

 as to much more than compensate its cost : it is not that the 

 decline of Genesis is less than proportionate to the increase of 

 Individuation, but there is no decline at all. Com- 



parison of the Rat with the Mouse yields a parallel result. 

 Though they difier greatly in size, yet the one is as prolific 



