GROWTH. 141 



kingdom, are, though large compared with their prey, small 

 as measured by other standards; even when aggregated into 

 groups of many individuals, which severally catch food for 

 the common weal, they are often so inconspicuous as readily 

 to be passed over by the unobservant. And if from this 

 point upwards we survey the successive grades of animals, it 

 becomes manifest that, in proportion as the size is great, the 

 masses of nutriment are either large, or, what is practically 

 the same thing, are so abundant and so grouped that large 

 quantities may be readily taken in. Though, for example, the 

 greatest of mammals, the arctic whale, feeds on such com- 

 paratively small creatures as the acalephes and molluscs 

 floating in the seas it inhabits, its method of gulping in 

 whole shoals of them and filtering away the accompanying 

 water, enables it to secure great quantities of food. We 

 may then with safety say that, other things equal, the 

 growth of an animal depends on the abundance and sizes of 

 the masses of nutriment which its powers enable it to appro- 

 priate. Perhaps it may be needful to add that, in 

 interpreting this statement, the proportion of competitors 

 must be taken into account. Clearly, not the absolute, but 

 the relative, abundance of fit food is the point; and this 

 relative abundance very much depends on the number of 

 individuals competing for the food. Thus all who have had 

 experience in fishing in Highland lochs, know that where 

 the trout are numerous they are small, and that where they 

 are comparatively large they are comparatively few. 



What is the relation between growth and expenditure of 

 energy? is a question which next presents itself. Though 

 there is reason to believe such a relation exists, it is not very 

 readily traced: involved as it is with so many other rela- 

 tions. Some contrasts, however, may be pointed out that 

 appear to give evidence of it. Passing over the vegetal 

 kingdom, throughout which the expenditure of force is too 

 small to allow of such a relation being visible, let us seek in 

 the animal kingdom, some case where classes otherwise 



