STUDIES IN AJSTIMAL LIFE. 65 



were got from the gutter of a house-top. Since 

 then they have been minutely studied, and have 

 been shown to be, not Infusoria, as Ehrenberg im- 

 agined, but Crustacea.* Your attention is request- 

 ed to the one point which has most contributed to 

 the celebrity of these creatures their power of re- 

 suscitation. Leuwenhoek described what you 

 have just witnessed, namely the slow resuscitation 

 of the animal (which seemed as dry as dust, and 

 might have been blown about like any particle of 

 dust) directly a little moisture was brought to it. 

 Spallanzani startled the world with the announce- 

 ment that this process of drying and moistening 

 of killing and reviving could be repeated fifteen 

 times in succession; so that the Rotifer, whose nat- 

 ural term of life is about eighteen days, might, it 

 was said, be dried and kept for years, and at any 

 time revived by moisture. That which seems now 

 no better than a grain of dust will suddenly awaken 

 to the energetic life of a complex organism, and 

 may again be made as dust by the evaporation of 

 the water. 



This is very marvelous; so marvelous that a 

 mind trained in the cultivated caution of science 

 will demand the evidence on which it is based. 

 Two months ago I should have dismissed the doubt 

 with the assurance that the evidence was ample and 



* See LEYDIG : Ueber den Bau und die systematische Stellung 

 der Rdderthiere, in SIEBOLD und KOLLIKER'S Zeitschrift, vi., and 

 Ueber Hydatina Senta, in MULLER'S Archiv, 1857. 



