426 Mr. Alfred Rti.ssel Wallare [Jan. 22, 



that the adaptation of every existin<^ species to its environment was 

 not only special but generaL The seasons changed from year to 

 year, but the extremes of change only occurred at long intervals, 

 perhaps of many centuries, with lesser, but still very considerable 

 variations twice or thrice in a century. It Avas by the actiou of these 

 seasons of extreme severity at long intervals, Avhether of arctic 

 winters, or summer droughts, that the very existence of species was 

 endangered ; and it was at such times that the enormous population 

 of most species and their wide range over whole continents, always 

 secured the preservation of considerable numbers of the best adapted 

 in the most favoured localities. Then the rapidity of multiplication 

 came into play, so that in two or three years the population of each 

 species became as great as ever : while, as all the least favourable 

 variations had been destroyed, the species as a whole had become 

 better adapted to its environment than before the almost catastrophic 

 destruction of such a large proportion of them. 



It is the fact of the adaptation of almost all existing species to a 

 continually fluctuating environment — fluctuating between periodical 

 extremes of great severity — that has produced an amount of adapta- 

 tion that in ordinary seasons is superfluously complete. This is shown 

 by the well-known fact that large numbers of adult animals that have 

 not only reached maturity but have also produced oif spring and 

 successfully reared them, continue to live and breed for many years 

 in succession, although varying considerably from the mean, while 

 almost the whole of the inexperienced young fall victims to the 

 various causes of destruction that surround them. ■ 



Tlie Nature of Adaptation. 



The next subject discussed was the complex nature of adaptations 

 in many cases, and probably in all ; a subject of great extent and 

 difficulty. The lecturer directed special attention to the relations 

 between the superabundance of vegetation in spring and summer, 

 the enormous, but, to us, mostly invisible, hosts of the insect tribes 

 which devour this vegetation, and the great multitudes of our smaller 

 birds whose young are fed almost exclusively on these insects. With- 

 out these hosts of insects the birds would soon become extinct ; w^hile 

 without the birds, the insects would increase so enormously as to 

 destroy a considerable amount of vegetable life, which would, in its 

 turn, lead to the destruction of much of the insect, and even of the 

 highest animal groups, leaving the world greatly impoverished in its 

 forms of life. 



The vast numbers of insects required daily and hourly to feed 

 each brood of young birds was next referred to, and the wonderful 

 adaptation of each kind of parent bird which enables it to discover 

 and to capture a sufficient quantity immediately around its nest, in 

 competition with many others engaged in the same task in every 



