90 Scientific Proceedings, Royal Dublin Society. 



structural development of such organisms as have to contend with 

 a niggardly, or hostile environment, reveals the same principle. 

 On'jthe pother hand some parasitic animals, to whom economy is 

 not so essential, grow into unwieldly dimensions. Animals living 

 immersed in the good-conducting medium, water, in general assume 

 its temperature ; and those warm-blooded animals exposed to 

 climatic rigour, clothe themselves with non-conducting coverings. 

 Reckless^ expenditure will not do. The environment, for all the 

 limitless ingenuity of the organism, sooner or later, fails to supply 

 the energy which creates its own demand, and the most rigorous 

 economy is exacted. 



We well know that the abundance of the ants and pines is not 

 a tithe of the abundance around us visible and invisible. It is a 

 vain endeavour to realise the countless numbers [of our fellow- 

 citizens 'upon the earth ; but for our purpose the restless ants, and 

 the pines solemnly quiet in the sunshine, have served as types of 

 animate things. In the pine the gates of the organic have been 

 thrown"open that the vivifying river of energy may flow in. The 

 ants and the butterflies sip for a brief moment of its waters, which 

 are the waters both of life and of death. On its banks we see the 

 vision of life^as of forms waxing and waning : a species victorious 

 in the^discovery of a new weapon, or by a new means of deceiving; 

 and^the equilibrium of the past is destroyed. A conquered species 

 must^yield and dwindle before a conqueror. 



The'old displaced by the young seek life in vain. Others fall 

 before unpitying foes; and so, mingled with the happy murmur 

 by the river'" of life, we hear that " chorus of sighs and groans of 

 despair, such as Dante heard at the gates of Hell." ^ 



It is significant to our present inquiry that these mingling 

 voices hail the sun at his rising, sink into silence at his setting, 

 and so pursue, as it were, his flight round the earth. 



1 Huxley. 



