32 F. G. HALL. 



living in the sand of roof gutters could be completely dried out 

 without losing vitality. Baker (1764) revived nematodes after 

 they had been in a dried state for twenty-seven years. Doyere 

 (1842) found that Tardigrada could endure higher temperatures, 

 as well as extreme exsiccation, without injury and in many cases 

 were able to live even in the absence of oxygen. Semper (1881) 

 tells of experiments with Apiis and Cypris eggs, which he kept in 

 a chest of dried mud for six years. He was able to hatch out 

 larvae in summer or winter by adding water to the mud. Semper 

 did not believe, however, that the eggs of the many animals that 

 endure extreme exsiccation lose all their water, but that the in- 

 tegument of the egg does not permit the complete removal of 

 water. 



Professor W. S. Marshall has kept Trogoderma larvae alive for 

 more than five years in vials without food or water. Wodsedalek 

 (1921) carried out similar experiments with the same species. 

 The larvae moulted but became smaller after each moult. They 

 did not eat their moulted skins. In Nature's larger laboratory 

 there are many cases of adaptation of animals to a dry environ- 

 ment. Protozoa and other microscopic forms encyst themselves 

 when ponds dry out. Thus they resist in a motionless state the 

 hot dry winds of summer, but revive again in spring when ponds 

 are filled with water. Spores of bacteria are extremely resistant 

 to exsiccation, living for days on dry glass. Desert lizards live 

 in extremely dry places. In fact, a number of animals live in the 

 driest places on earth. 



While there are many experiments to show the effects of exsic- 

 cation most of them have been with simpler or smaller animals. 

 Because of the microscopic size of these no quantitative results 

 could be obtained. It would seem improbable that an animal can 

 remain active after losing all its water, or that all the water could 

 be removed from an organism without causing death. Thus it is 

 important to study comparatively the amount of water that can 

 be removed from animals without loss of vitality. Schmidt 

 (1918) found that earthworms can revive and apparently become 

 perfectly normal after a loss of 61.8 per cent, of the body weight, 

 or nearly 73 per cent, of the weight of the water contained in the 



