128 THE INDUCTIONS OF BIOLOGY. 



the differences between the sizes of organisms, has yet to hi- 

 considered. We are introduced to it by pushing the above 

 inquiry a little further. Small animals have been shown to 

 possess an advantage over large ones, in the greater ratio 

 which, other things equal, assimilation bears to expenditure; 

 and we have seen that hence, small animals in becoming 

 large ones, gradually lose that surplus of assimilative power 

 which they had, and eventually cannot assimilate more than 

 is required to balance waste. But how come these animals 

 while young and small, to have surplus assimilative powers ? 

 Have all. animals equal surplus of assimilative powers ? 

 And if not, how far do differences between the surpluses de- 

 termine differences between the limits of growth ? We 

 shall find in the answers to these questions, the interpretation 

 of many marked contrasts in growth that are not due to any 

 of the causes above assigned. For example, an ox immensely 

 exceeds a sheep in mass. Yet the two live from generation 

 to generation in the same fields, eat the same grass and tur- 

 nips, obtain these aliments with the same small expenditure 

 of force, and differ scarcely at all in their degrees of organiz- 

 ation. Whence arises, then, their striking unlikeness of bulk ? 



We noted when studying the phenomena of growth in- 

 ductively, that organisms of the larger and higher types, com- 

 mence their separate existences, as masses of organic matter 

 having tolerable magnitudes. Speaking generally, we saw 

 that throughout each organic sub-kingdom, the acquire- 

 ment of great bulk occurs only where the incipient bulk 

 and organization are considerable ; and that they are the 

 more considerable in proportion to the complexity of the life 

 which the organism is to lead. 



The deductive interpretation of this induction may best bo 

 commenced by an analogy. A street orange-vendor makes 

 but a trifling profit on each transaction; and unless more 

 than ordinarily fortunate, he is unable to realize during 

 the day a larger amount than will meet his wants : leav- 

 ing him to start on the morrow in the same condition aa 



