ZOOLOGY. 479 



lived therein. " Observations 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, IIow?" 



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

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

 allowed to dry, invariahly 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% iviflcatiou on the reap^ 

 pearance of rain, but to the peculiar character of the eggs, whicli de- 

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

 led most deciijedly to the conclusion that the desiccated forms in their 

 mature condition, always 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 nematoid worms after des- 

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

 likewise applicable to i^lants. Thus, according to Professor Zacharias, 

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

 nosphcvra " explain the persisteiice of these algoid forms in the jiool." 

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

 real fauna and flora rediviva." (Biol. Centralbl., vi, pp. 230-235 5 J. 

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



Minimum life temperatures. — A series of experiments upon various 

 animals has been made by Dr. II. von Ihering in extension of Professor 

 Pouchet's researches on the resistance which animals may otfer to cold. 

 About two dozen 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 curve, 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. 183-2U5 J. It. M. S., 1887, vii, p. 52.) 



