764 LIFE : OUTLINES OF GENERAL BIOLOGY 



some fish pass through their grilse stage without ascending the 

 rivers to spawn. Indeed, they may remain in the sea till they are 

 five or six years old. 



The life-story of the salmon varies in detail in different rivers, 

 and is still far from being well understood biologically. But, in any 

 case, there is a very marked alternation between nutrition and 

 reproduction. During the nutritive period in the sea, the fish feed 

 on herring, mackerel, sand-eels, some crustaceans, and the like, 

 accumulating great stores of potential energy, part of which is 

 afterwards expended in swimming against the stream and ascending 

 the rapids. The period in fresh waters is for the adults a time of 

 fasting, more or less strictly observed. But this time of fasting is the 

 time for pairing and multiplying; and here we have a familiar in- 

 stance of the swing of the vital pendulum: "A time to tear down 

 and a time to build up; a time to preserve and a time to throw 

 away; a time to embrace and a time to refrain from embracing." 

 Let us repeat ourselves: Whether we think of foliage and flowering, 

 or of the voracious caterpillar and the ascetic butterfly, it is the 

 same fundamental antithesis: "A time to seek and a time to lose," 

 an alternation of relatively preponderant anabolism and relatively 

 predominant katabolism. But is there any illustration more dramatic 

 than the contrast between the maiden fish and the spawned kelt? 

 For after the reproduction there is exhaustion and debility, and 

 many drift tail foremost downstream. Even in the short Scotch 

 rivers there is considerable mortality, so that it is not surprising 

 that in the longer rivers of the Pacific Coast, where the up- 

 stream journey may extend to a thousand miles, those that go far 

 never survive reproduction. Thus while our European species often 

 succeeds in evading the nemesis that tends to follow reproduction, 

 and may reach an age of even eight years, there is in the Pacific 

 species the same vertical drop of the curve that we noticed in Mayfly 

 and lamprey. 



As a sharp contrast to life-curves in which the youthful stages are 

 prolonged take the case of the Mound-Birds of Borneo, where the 

 whole of the chick period has been telescoped. The eggs are laid in 

 heaps of fermenting vegetation, or are sometimes buried near hot 

 springs ; and there is nothing of the nature of brooding or watchful 

 care. When the young bird scrambles out of the egg-shell it in- 

 stinctively continues its struggles and frees itself from the mound. 

 Observers tell us that if it should become thoroughly exhausted in 

 the process and cease to struggle, it cannot resume its efforts and 

 must perish miserably. This is a common feature in instinctive 

 behaviour, that interruptions are apt to prove fatal. In most cases, 

 however, the young Mound Bird succeeds, and an hour after hatching 

 it is fending for itself in the scrub. In some cases it flies on the day 

 of its hatching! It passes out of the egg into the tasks of everyday 



