204 
AERIAL AND TERRESTRIAL DIPTERA. 
comparison is a mode of description , and not an explanation. I said: 
“ What is Life ? On this question I adhere, at least in the present 
state of our knowledge, to the humble avowal of Prof. Du Bois- 
Reymond : ‘ Ignorabimus ’! ” 
The distinguished French thinker Rivarol (1754-1801), in his 
“ Maximes et Pens^es,” has formulated the same idea in the follow¬ 
ing sentence: — 
“Des qu’on a nomine la nature, il n’y a plus probleme, mais 
mystere; il lie s’agit plus d’expliquer, mais d’exposer.” 
