PHENOMENA AND CONDITIONS OF LIFE 



39 



to dryness. All these phenomena we have to regard as perfect 

 adaptations to the conditions of life, for as these animalcules 

 have to sustain in their normal habitation, the roof-gutter, not 

 only frequent changes of moisture and dryness, but also, 

 unprotected, the heat of the sun and the cold of winter, life 

 without such high power of resistance would to them become 

 impossible. 



PIG. 11. THE MUD-FISH (Protopterus Annectens). ON THE LEFT, A FISH BESTING 



IN ITS MUD-SHELL. 



Cases of ' dry-coma ' are known even among the higher 

 animals. The best instance is that of the mud-fishes or Dipnoi, 

 a small order of fishes that do not only breathe through gills 

 but also through lungs, the air-bladder having become trans- 

 formed into a single or double lung. When the dry weather 

 comes these curious animals build out of mud and slime a solid 

 shell in which they roll themselves up and pass the dry period, 

 apparently quite dead. As this state lasts for several months it 

 has been found possible to bring them, shell and all, to Europe. 



