CH. XII INSECTS OF THE SEA-SHORE 371 



mental evidence, but merely upon vague impressions. 

 Had it come into the minds of the naturalists of 1820 

 to make the trial which Plateau made in 1872, they 

 would have better appreciated the hardiness of ter- 

 restrial Arthropods, and the ease with which they 

 submit to hours and even to days of submersion in 

 water. Plateau took a number of land Beetles of 

 various kinds, devoid of special organs for carrying 

 down a supply of air, and found that they could 

 endure complete immersion in fresh water for two, 

 three, or even four days. The Beetles became torpid, 

 but recovered on being restored to the air.^ Many 

 aquatic Insects, which dive with the greatest ease, do 

 not survive more than a very few hours under like 

 conditions. Gyrinus struggles violently when detained 

 beneath the surface, and perishes in about three 

 hours, while Aphodius becomes perfectly still and 

 senseless, but recovers after an immersion of fifty 

 hours.2 



Insects submerged in water behave as a rule like 

 Insects placed in an atmosphere devoid of free oxy- 

 gen. They cease to struggle in a few moments, and 

 pass into a state of torpor, which may be greatly 

 prolonged without fatal results. Certain larvae and 

 pupae live for weeks or months buried deep in earth 

 or in vegetable refuse. It is almost impossible to 

 kill certain Insects in a moderate time by carbonic 



^ Rech. physico-chimiques sur les Articulds aquatiques {Bull. 

 Ac. Roy. Belg. 1872). 



^ Gyrinus is an Insect of much more active habits than 

 Aphodius, and the aquatic Insects experimented upon by 

 Plateau are in general more active than the terrestrial species. 



B B 2 



