68 The Naturalist in La Plata. 



tliat in spring it was hard to find a survivor, even 

 in the barns and houses. The fact that species 

 tend to increase in a geometrical ratio makes these 

 great and sudden changes frequent in many regions 

 of the earth ; but it is not often they present them- 

 selves so vividly as in the foregoing instance, for 

 here, scene aEter scene in one of Nature's silent 

 passionless tragedies opens before us, countless 

 myriads of highly organized beings rising into 

 existence only to perish almost immediately, scarcely 

 a hard-pressed remnant remaining after the great 

 reaction to continue the species. 



