128 SURVEY OF INVERTEBRATES 



water is a well-known fact (see e.g., Basse, 1905; Mar- 

 cus, 1928; Baumann, 1929) which has been much used in 

 morphological studies since the animals then become ex- 

 tended and are well suited for observation. It seems that 

 during the asphyxiation process the epithelial cells lose 

 the ability to regulate their water content and swell up; 

 this phenomenon seems to be without parallel in other 

 animals. The time necessary for a tardigrade to reach 

 the asphyctic state depends upon the temperature; at 

 17° C. it takes about 2 days. At 27°, however, this stage 

 is never attained, the animals die in a few hours due to 

 lack of oxygen. The asphyctic stage, once reached, is en- 

 dured for relatively short periods only, by Milnesium, 

 for example, for about 3 days (Baumann, 1929). 



The behavior of dry specimens is in marked contrast 

 with that of moist ones. They exhibit an extremely high 

 resistance to lack of oxygen. Rahm (1929) and Becquerel 

 (1936) kept them in this condition for wrecks or even 

 months and found that the animals revived upon restor- 

 ation of suitable conditions. The explanation is, of 

 course, the same as that given in a previous chapter for 

 dry nematodes. Dry tardigrades are in a stage of vita 

 minima or even in suspended animation, and therefore 

 need only infinitesimal amounts of oxygen, or none. 



Little information is available for chilopods and diplo- 

 pods. In a few experiments of immersion in water by 

 Plateau (1890) and Rossi (1901) they survived a re- 

 markably long time ; Geophilus longicornis, for example, 

 survived 15 days (Plateau). Rossi, however, pointed 

 out that these experiments do not prove much since the 

 animals are capable of a considerable aquatic respira- 

 tion. He himself carried out some experiments with inert 

 gases. Lithohius forficatus survived only a few hours; 

 Julus terrestris was much more resistant, it could be 

 kept alive for more than five days in nitrogen. 



