140 THE INDUCTIONS OF BIOLOGY. 



great size. The proposition here illustrated is the converse 

 one, that great size is habitually accompanied by high 

 organization. The conspicuous facts that the largest species 

 of both animals and vegetals belong to the highest classes, 

 and that throughout their various sub-classes the higher 

 usually contain the more bulky forms, show this connexion 

 as clearly as we can expect it to be shown, amid so many 

 modifying causes and conditions. 



The relation between growth and supply of available 

 nutriment, is too familiar a relation to need proving. There 

 are, however, some aspects of it that must be contemplated be- 

 fore its implications can be fully appreciated. Among 

 plants, which are all constantly in contact with the gaseous, 

 liquid, and solid matters to be incorporated with their tissues, 

 and which, in the same locality, receive not very unlike 

 amounts of light and heat, differences in the supplies of 

 available nutriment have but a subordinate connexion with 

 differences of growth. Though in a cluster of herbs spring- 

 ing up from the seeds let fall by a parent, the greater sizes 

 of some than of others is doubtless due to better nutrition, 

 consequent on accidental advantages; yet no such inter- 

 pretation can be given of the contrast in size between these 

 herbs and an adjacent tree. Other conditions here come 

 into play : one of the most important being, an absence in 

 the one case, and presence in the other, of an ability to 

 secrete such a quantity of ligneous fibre as will produce a 

 stem capable of supporting a large growth. Among 

 animals, however, which (excepting some Entozoa) differ 

 from plants in this, that instead of bathing their surfaces 

 the matters they subsist on are dispersed, and have to be 

 obtained, the relation between available food and growth 

 is shown with more regularity. The Protozoa, living on 

 microscopic fragments of organic matter contained in the 

 surrounding water, are unable, during their brief lives, to 

 accumulate any considerable quantity of nutriment. Polyzoa, 

 having for food these scarcely visible members of the animal 



