EXTERMINATION IN ANIMAL LIFE. 337 



to the Eev. G. Henslow from Olot (Genova) that in consequence 

 of a great drought such a transformation took place in a plant 

 of Rosa sepium that it became unrecognizable. "The stalks, 

 leaves, and flowers were reduced to half their size, the stems 

 became much more thorny, the leaves, calyces, and flowers much 

 more glandular." * 



Estimating the natural phenomena of the past by our know- 

 ledge of those of the present, as we are compelled to do by the 

 limits of our experience and intelligence, we may conclude that 

 certain sporadic loss in animal life occurred then as now,t and 

 of which we have not the particulars or summary. Such was a 

 scarcity and epidemic among insects at Chontales recorded by 

 Belt in 1872, and of Wasps in North Wales in 1865.1 Many 

 records exist, and are frequently made both in these islands and 

 on the Continent, as to years of scarcity in insect life, though this 

 cannot of itself be considered in the light of an exterminative 

 process, for often a prolific follows a meagre entomological year, 

 but it is not difficult to imagine that should such a year of 

 scarcity in insect life be also a year of great drought, or be 

 attended or succeeded by a period of other disadvantages, then 

 such a diminution in numbers to contest excessive mortality 

 would probably prove fatal to many species. These coincidences 

 must sometimes occur in the struggle for existence; it is not the 

 adverse circumstances, or the single malady, which is difficult 

 to conquer ; but when adversity occurs in manifold directions, 

 or an illness assumes the form of a complication of diseases, 

 then the society or the individual succumbs. All life, including 

 that of man, can only bear a certain strain ; a central attack 



* ' The Origin of Plant Structures,' p. 47. 



f Of course this is a postulate requiring great qualification ; for, as the 

 late Sir J. F. Stephen argued, "All our anticipations involve an assumption 

 utterly incapable of proof, that the future will resemble our present concep- 

 tion of the past." — (" Necessary Truth " ; ' Contemporary Eeview,' vol. xxv. 

 p. 73.) 



I 'Naturalist in Nicaragua,' pp. 180 and 181. — With Wasps, however, 

 as recorded by Mr. Norman, "It is a curious fact that occasionally when 

 queen Wasps have been unusually numerous in the spring,- and there is 

 every reason to expect a great abundance of Wasps, there are nevertheless 

 very few in the autumn ; while in other years, as in the case now (1851), 

 after having had apparently a great paucity of queens, Wasps are very 

 numerous." — (' Zoologist,' vol. ix. p. 3236.) 

 Ziooi. -ith set. vol. IX., September, 1905. 2 D 



