134 Naturalist in La Plata. 
occurring in 1816 , and extending over a large por- 
tion of Europe. But in tliese cases the movement 
took place at the end of May, and the insects 
travelled due south ; their migrations were there- 
fore similar to those of birds and butterflies, and 
were probably due to the same cause. I have 
been unable to find any mention of a phenomenon 
resembling the one with which we are so familiar 
on the pampas, and which, strangely enough, 
has not been recorded by any European naturalists 
who have travelled there. 
