COCKROACHES, ETC. 119 



violent struggles. This is quite in accordance with 

 some experiments carried out by Professor Plateau, 

 of Ghent, on aquatic and terrestrial insects ; the 

 Belgian savant found that terrestrial insects can sus- 

 tain total immersion for prolonged periods 22 J hours 

 to 97J hours ; they may present all the appearance of 

 death, but they soon recover when removed from the 

 water. Aquatic insects, such as Water-Beetles and 

 Water-Boatmen, on the other hand, when placed in 

 water and denied all access to air, struggle violently 

 and soon drown, for when removed from the water 

 they do not recover. 



It was concluded from the above-described observa- 

 tions that aquatic insects by their violent struggles 

 rapidly exhaust all the air contained in the tracheae, 

 or breathing-tubes, ramifying throughout their bodies, 

 and, being unable to renew the supply, they become 

 asphyxiated ; whereas terrestrial insects do not struggle 

 so violently when immersed in water, and consequently 

 do not use up their supply of air at once. From 

 such experiments and observations as I have made, I 

 do not believe that this explains the whole secret of 

 the endurance shown in water by terrestrial insects. 

 In the first place a typically terrestrial insect, such as 

 the common Cockroach of Borneo, Periplaneta aus- 

 tralasice, when immersed in water will struggle quite 

 as violently as the aquatic species, and yet will endure 

 total immersion for some hours before finally suc- 

 cumbing. If a Periplaneta be thrown into a basin of 

 water it flounders about on the surface, and all its 

 efforts will not suffice to take it under the surface ; 

 even when the wings and wing-covers, which con- 

 ceivably might help to buoy it up, are removed, the 



