66 WITH HARD CHEEKS. 



genus Cottua just described have large heads and wide 

 gill-pertures ; yet of them it is said (tome iv. p. 159), " Ces 

 chaboisseaux vivent tres long-tems hors de Teau." 



Of fishes with large gill-apertures it is said, in the same 

 work (tome i. p. 519), that they die, " non pas faute 

 d*'oxigene, mais parce que leurs branchies se dessechent ;" 

 and of the Herring, that they die the instant they are 

 taken out of the water. But may it not be objected to 

 this view, that desiccation of the gills could not take place 

 in so short an interval of time, and therefore could not be 

 the cause of death ? Dr. Monro calculated that the surface 

 of the gills in a large Skate was equal in extent to the 

 whole surface of the body of a man ; yet, with this extent 

 of surface exposed to the effects of desiccation, the different 

 species of Skate are remarkable for the length of time 

 they are able to sustain life after they are removed from 

 water. Of fishes with small gill-apertures, our common Loche 

 Cohites jluviatilis, and our most common species of the genus 

 Callion^mus, both die quickly. The Father-Lasher, with 

 its large gill-aperture, will live a long time out of water, as 

 has been already noticed ; yet, when taken out of the sea, 

 if put into fresh water, it dies instantly.* The reverse of 

 desiccation takes place in this instance : the gills are bathed 

 with a fluid containing more oxygen than sea-water, and 

 which also yields that oxygen much easier, yet death hap- 

 pens immediately. In this last instance it may be inferred 

 that the fish, unable suddenly to accommodate its respiratory 

 organs to fluids of such different densities as those of pure 

 sea and fresh water, the blood is imperfectly aerated, the 

 brain is affected, convulsions ensue, and, if not released, it 

 soon dies ; and, from the previous examples, may we not 



* Loudon's Magazine of Natural History, vol. ii. p. 217 and 218. 



