APPENDIX. 285 



this faculty has its limits, and each experiment generally 

 proves fatal to one or more individuals. Thus in alter- 

 nately drying and moistening the same sand, we shall find 

 that on each repetition of the process a smaller number 

 of animalcules come to life. Spallanzani in his experi- 

 ments on the Rotifers did not find that any of them re- 

 vived after the sixteenth alternation of draught and 

 humidity; Paste-eels, however, bore seventeen of these 

 experiments.* This diminution of the singular faculties 

 possessed by these animals is equally apparent after they 

 have been kept for a long period of time. Spallanzani, 

 after having well dried some sand, which was very rich 

 in Rotifers, kept it for more than three years, merely 

 moistening some portions of it every five or six months. 

 He found that the number of individuals which were 

 thus resuscitated, continued to diminish progressively, 

 and it is much to be regretted that this able observer did 

 not continue his experiments somewhat longer. Baker, 

 however, who after Needham continued to observe Paste- 

 eels, went still farther ; for he kept the paste from which 

 they had been taken, without moistening it in any way, 

 for twenty-seven years, and at the end of that time he 

 found that the eels revived on being immersed in a drop of 

 water. If they had exhausted their life all at once, and 

 without any intermissions, these Rotifers and Paste-eels 

 would not have lived beyond sixteen or eighteen days. 



* These Anguillulse, whose name alone is sufficient to indicate 

 their general form, were discovered by Needham, a distinguished 

 naturalist of the eighteenth century. He was born in 1713, and 

 successively resided at Lisbon, London, and Paris, where he occu- 

 pied himself with microscopical investigations conducted under the 

 directions of Buffon. Having been called to Brussels to direct the 

 organisation of the Academy which had been founded by Maria 

 Theresa, he settled in that city, and remained there until his death 

 in 1781. 



