260 THE BEGINNINGS OF LIFE. 



materials employed was invariably accompanied by the 

 appearance of different organisms these being often- 

 times strange and peculiar, and unaccompanied by any 

 of the familiar forms. Even Ehrenberg himself was 

 obliged to admit the difficulty of obtaining similar 

 infusoria in apparently similar infusions ; and Burdach 

 also records the fact that the characters of these animals 

 vary with the medium, and with the conditions under 

 which they exist. Dujardin, too, one of the more 

 recent systematic writers, acknowledges the great 

 difficulty there is in establishing zoological distinctions 

 between these animals. He refers to the Paramecia, more 

 especially, as forms which are prone to undergo the 

 greatest variation under the influence of the smallest 

 change of conditions. M. Pouchet, moreover, says 

 he has continually seen new forms arise in solutions, 

 which never again presented themselves to his ob- 

 servation, even in the course of years. The mor- 

 phological diversity of these animals is so great that 

 it is always extremely difficult, and often quite im- 

 possible, to determine their names. c Sometimes/ he 

 adds \ c a multitude of different forms appear even 

 in a single experiment. Thus in a maceration of some 

 fragments of human bone, which I had brought from 

 the catacombs of Thebes, and which had remained 

 three months in water, I saw the greater number of 

 the Vorticellae of our French fauna present themselves 

 at once, and in addition a great number of other forms 



1 c Heterog&iie,' p. 412. 



