M. F. Plateau on the Aquatic Articulata. 71 



over the orifice of the latter, in such a way that an insect placed 

 in this smaller vessel is actually in the general mass of water, 

 but cannot rise to its siu'face. 



Ten'estrial insects placed in these conditions ascend, carried 

 by their specific levity, till they rest against the lower surface 

 of the net ; the movements of their feet soon cease, they do not 

 seem to suffer, and quickly become insensible. The aquatic 

 Coleoptera and Hemiptera on the contrary, instead of sub- 

 mitting passively to their fate, seek to escape from their prison, 

 swim about rapidly, endeavour to rise to the surface, and con- 

 tinue their agitation until their forces become weakened, and 

 they finally remain as if dead at the bottom. 



To cause an insect which has been subjected to a prolonged 

 immersion to recover froraits state of insensibility, it is necessary, 

 after taking it out of the water, to dry it Avith bibulous paper. 

 If the dm-ation of the submersion has not exceeded a certain 

 limit, the animal gradually recovers its original activity, the 

 trial it has undergone leaving no sensible ti-aces upon it. 



These experiments were of course repeated as much as 

 possible upon several individuals and with different durations, 

 so as to ascertain for each species the limit of time after which 

 the insect was actually dead. I have thus arrived at the fol- 

 lowing two curious conclusions, which are supported by a 

 great number of experiments. 



1. Terrestrial Coleoptera resist complete submersion during 

 a very long time (from three to fom* days). For example, 



Oryctes nasicornis resists a submersion of 96 hours. 

 Agelastica alni ,, „ 72 „ 



Carabus auratus „ „ 71 h. 30 m. 



2. Natatory aquatic Coleoptera and Hemiptera, far from 

 presenting a greater resistance to asphyxia by submersion, are 

 no better endowed in this respect than terrestrial insects, and 

 even perish in most cases much more rapidly. I cite the fol- 

 lowing numbers from the tables in my memoir : — 



A Dytiscus marginalis ^ died at the end of 65 h. 30 m. 



An Acilius sulcatus ? „ „ 24 hours. 



A Nepa cinerea „ „ 31 „ 



A Notonecta glauca „ ,, 3 „ 



The cause of this unexpected inferiority of the aquatic in- 

 sects seems to consist exclusively in their greater activity in 

 the water, and consequently in a more rapid expenditure of 

 oxygen. 



II. Influence of cold: effects of congelation. 

 What is the lowest temjicraturc that the aquatic Articulata 



