EXPERIMENTS UPON DYTICUS MARGINALIS. 177 



Felix Plateau, Paul Eeguard, Charles Eichet, Henry de Varigny, 

 Ernile Yung, &c. I ought to add that all my experiments have 

 been conducted with healthy males and females of Dyticus 

 marginalis, and I have registered the temperature of the water 

 with a Centigrade thermometer. 



Dyticus marginalis possesses great vital endurance, and, in 

 making experiments upon it, it is very important not to allow 

 oneself to be deceived by its apparent death. In fact, I have 

 had occasion to observe several times in the course of my experi- 

 ments that individuals which appeared dead, and for several 

 days manifested their existence only under the influence of 

 mechanical stimuli, were able nevertheless to return to life. 



Action of cold. — Everyone knows that the ponds and ditches 

 of northern countries which Dyticus marginalis inhabits are 

 covered, during the cold season, with a mantle of ice more or 

 less thick, which remains sometimes for weeks without melting, 

 though without at all occasioning the death of the Dytici. Do 

 these insects, despite the lowering of the temperature, retain 

 their noAaal activity, and consequently respire as actively ; or, 

 on the other hand, does the cold lessen their activity to a greater 

 or less degree, as in the majority of insects, which then consume 

 much less oxygen ? 



The fact that the Dytici which live in water of which the 

 temperature is only 3° or 4° are quite as lively as if it was at its 

 habitual temperature of the warm season — a fact which I have 

 observed several times — leads one to think that at the tempera- 

 ture of melting ice the activity of these insects remains identi- 

 cally, or almost identically, the same. I wished to have the 

 experimental proof of this. I therefore placed the Dytici in a 

 large glass bowl, which I filled entirely with pieces of ice, and 

 placed in a situation where the temperature was low, so that the 

 ice melted slowly. Four days after there was still a small frag- 

 ment of ice in the bowl, which proves that the temperature of 

 the water had remained very near freezing-point. During these 

 four days my insects showed themselves quite as active as at the 

 mean temperature of the water in which they live. I obtained 

 the same result by placing other examples of D. marginalis in a 

 bowl filled with water which I surrounded completely with bits 

 of ice, and left outside for two days during the cold. The con- 

 gelation of almost the whole surface proved to me that the water 

 in which my insects were swimming was at a temperature 

 sensibly equal to 0°. 



To sum up, the temperature of melting ice does not render 

 Dyticus at all torpid, and consequently, when the surface of the 

 water where they live is not completely frozen, these Coleoptera 

 consume the usual quantity of oxygen. 



Action of want of atmospheric air. — What happens when the 

 surface of the pond is frozen over its whole extent, so that the 



