GROWTH. 1 13 



bers of tlie animal kingdom, are, thougli large compared 

 with their prey, small as measured by other standards : even 

 when aggregated into gronps 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 successi^^e 

 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 as that large quantities may be readily taken in. 

 Though, for example, the greatest of mammals, the arctic 

 whale, feeds on such comparatively 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 appropriate. Perhaps it may be 



needful to add that, in interpreting this statement, the 

 number 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 how many individuals are competing for the food. Thus 

 all who have had experience of fishing in Highland lochs, 

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

 that where they are comparatively large they are compara- 

 tively few. 



What is the relation between growth and expenditure cf 

 force? 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 



