180 THE ENTOMOLOGIST. 



they were very active, one observes precisely the same effects as 

 in the sudden passage from cold to hot water. These insects 

 usually swim for a few seconds, after which they become motion- 

 less and appear dead ; then little by little they stir all their legs, 

 and finally recover their normal activity in this water at 5°. 



To be precise, my experiments upon the action of heat on 

 Dyticus marginalia show that temperatures of water very near 

 40° are those in which this coleopteron can live only for a more 

 or less short time, and also that the immobility of the Dytici, 

 previously very active, is manifested in the same manner in the 

 sudden passage from cold to hot water, or vice versa. 



Action of chloride of sodium. — The endurance of Dyticus 

 marginalia in saline water is very great. In fact, I have kept in 

 1000 grammes of water containing 50 grammes of sodic chloride 

 — that is to say, 5 per cent. — some Dytici which died only seven- 

 teen days after, others having succumbed after a shorter lapse of 

 time. Now, 5 per cent, is twice the quantity of marine salt 

 contained in the water of the temperate parts, at least, of the 

 Atlantic Ocean. Moreover, the Dytici were dead only at the 

 end of nine days in water containing 10 per cent, of sodic 

 chloride. It should be added that during the first third of the 

 duration of these experiments my Dytici appeared very little 

 incommoded by the surrounding medium. 



I observed that in water containing 5 per cent, of chloride of 

 sodium, Crested and Palmated Tritons, both species adult and 

 very vigorous, were dead at the end of four hours, and that, in 

 water containing 10 per cent, of it, they succumbed in less than 

 an hour, the Crested Tritons dying much less rapidly than the 

 Palmated Tritons, which are smaller. 



Action of chloride of magnesium. — I wished also to note the 

 injurious action upon Dyticus of this salt, which iu a general 

 manner comes immediately after sodic chloride, in point of 

 view of quantity, in the composition of the water of the seas of 

 our planet. 



The experiments which I have made to this end permit me 

 to say that the resistance of Dyticus marginalia to the action of 

 magnesic chloride is sensibly the same as its resistance to sodic 

 chloride. 



In water containing 5 per cent, of magnesic chloride, some 

 individuals perished only at the end of nineteen days, and in 

 water containing 10 per cent, of it the Dytici died only after 

 living nine days. I ought to add that other individuals suc- 

 cumbed there in a much shorter time. 



Some very vigorous adult Palmated Tritons were quite dead 

 at the end of an hour in water containing 5 per cent, of magnesic 

 chloride, and, what goes without saying, more rapidly still in 

 water containing 10 per cent. 



In my opinion the great endurance of Dyticus marginalis in 



