ZOOLOGY. 479 



lived therein. " Observ^ations made nearly fifty years ago indicate the 

 presence at that date of a similar fauna, and there is every reason to 

 believe that at least for a century similar forms have tenanted the cavity. 

 Thus the fauna has persisted in spite of complete desiccation — thousands 

 of times repeated. The problem is, Howf" 



In order to solve this problem, Professor Zacharias instituted a num- 

 ber of experiments, and found that the Philodina and tardigrade, ''when 

 allowed to dr}', invariably died,'''' but tlie ova were preserved from death 

 by encystation. The persistence of the fauna is therefore not due to 

 the survival of the adult animals, and their re^ ivificatiou on the reap- 

 pearance of rain, but to the peculiar character of the eggs, which dC' 

 velop with the returning rain. In fine. Professor Zacharias has been 

 led most decit'edly to the conclusion that the desiccated forms in their 

 mature condition, alwa^^s die, while the eggs may frequently survive. 

 These results are in accordance with those obtained by other experi- 

 ments, for example the non-revivification of neraatoid worms after des- 

 iccation, as was proved by Hallez. That which is true for animals is 

 likewise applicable to plants. Thus, according to Professor Zacharias, 

 the resting stage of Hccmatococcus and the zygospore stage of Stepha- 

 nospJuera " explain the persistence of these algoid forms in the pool." 

 The conclusion is that "there is therefore probably no such thing as a 

 real fauna and flora rediviva." (Biol. Centralbl., vi, pp. 230-235 ; J. 

 E. M. S. (2), VI, pp. 799-800.) 



Minimum life temperatures. — A series of experiments upon various- 

 animals has been made by Dr. H. von Iheriug in extension of Professor 

 Pouchet's researches on the resistance which animals ma^' offer to cold. 

 About twodozen worms, arthropods, and mollusks were made the subject 

 of investigation. The results have been summarized in the following 

 terms : 



(1) "Lower animals become frozen at temperatures varying greatly 

 in the different genera and species. The resistance varies with the 

 actual body heat of the animal, with its size, structure, and protective 

 covering, with the freezing point of the blood, etc." 



(2) "The resistance usually increases with progressive development, 

 but sometimes the adults are more sensitive than the young." 



(3) "Nothing can be directly inferred from the geographical distribu- 

 tion." 



(4) " Perfectly frozen animals are never revivified." 



Dr. von Ihering suggests a curv^e, with the degree and the duration 

 of the temperature as co-ordinates. These two factors must be consid- 

 ered together. The absolute minimum is obviously the fatal temper- 

 ature in unit time. He enumerates the various results, as exhibited by 

 degeneration, cessation of certain functions, sleep, like paralysis, and 

 death; and sums up his experiments in a tabular survey." (Zeitschr, 

 f. Naturwiss., lix pp. 183-2U; J. R. M. S., 1887, vn, p. 52.) 



