EXPERIMENTS UPON DYTICUS MARGINALIS. 179 



Action of heat. — In the study of this action upon Dyticus 

 marginalia, the experiments must be separated into two groups : 

 those in which the temperature has been increased or lowered 

 gradually, and those in which the Dytici have been plunged sud- 

 denly from cold water into hot water, or vice versa. 



From repeated experiments I have assured myself that by 

 gently increasing the temperature of the water in which the 

 Dytici are found one can bring it to temperatures of 30°-35° 

 without the insects appearing greatly inconvenienced. To afford 

 a basis of calculation, I will take the duration of about an hour 

 to make water of 5° pass to a temperature of 30° to 35°. Up to 

 30° the Dytici always retain their usual activity. It is from 

 30°-35° that they begin to suffer more or less strongly from the 

 temperature of the water : some swim more rapidly than ordi- 

 narily ; others try to leave the medium in which they are placed ; 

 others become more or less motionless. Be that as it may, I 

 have kept Dytici in water whose temperature was maintained at 

 35° for more than two hours ; and I do not doubt that, without 

 serious inconvenience to my insects, it would have been possible 

 for me to prolong the experiment for hours more, perhaps even 

 for days, with individuals of strong resisting powers. From 

 35°-40° the Dytici perish at the end of an obviously variable 

 time. At 40° they succumb usually at the end of about four 

 to ten minutes. At 50° their death ensues between one and 

 three minutes, and above 50° they always die very rapidly. If, 

 after having gradually increased the temperature of the water up 

 to a maximum of 40°, one then lowers it little by little to near 

 its original temperature, the Dytici endure the experiment 

 perfectly. 



If, instead of working by a progressive elevation and lowering 

 of the temperature, one suddenly plunges into water registering 

 30°-35° C. some Dytici which were in water at about 5°, these 

 insects, as I have observed, always swim more or less rapidly for 

 several seconds, after which they become motionless at the end 

 of one or two minutes at the most, then appear dead ; but little 

 by little they return to life, and regain all their activity at these 

 temperatures, which are very high for these insects. 



If the Dytici be plunged suddenly into water at 40°, 50°, or 

 upwards, the same phenomena are produced ; but it is very 

 evident that the rapidity of immobility and death is in direct 

 proportion to the elevation of the temperature. According to 

 my experiments, the Dytici that one passes without transition, 

 from water at about 5° to water at 40° or 50°, are quite dead 

 after remaining ten minutes in water at 40°, and five minutes in 

 water at 50°. 



If, instead of passing the Dytici at once from cold water to 

 hot, one suddenly plunges into cold water, say, at 5°, Dytici accus- 

 tomed to water possessing a temperature of 30° to 35°, in which 



