,8^. NOTES AND COMMENTS. 87 



after a long series of experiments, and the theory of " palingenesis " 

 passed into the rank of accepted truths : thus the name of rediviva 

 was frequently applied to new species by authors who might be 

 supposed to possess especial knowledge of the group. Hence it is 

 not surprising that the idea that Rip-van-Winkledom was a normal 

 condition of things among Rotifers should have gained widespread 

 popularity, and have done duty as one of the principal articles of the 

 stock-in-trade of successive generations of lecturers and writers on the 

 romance of natural history. 



So improbable a theory, however, was not allowed to pass 

 unchallenged, and Pouchet, in 1859, subjected it to very severe 

 adverse criticism. Fredericq, in 1889, and Zaccharias a year later, 

 also opposed it, while now Dr. F. Faggioli, of Genoa, has completely 

 demonstrated the erroneous character of the whole story.' He 

 has carried out a series of experiments conducted with the precise 

 methods of modern research, and has shown that a Rotifer, if once 

 properly dead or dried, cannot in any way be brought to life again. 

 Dr. Faggioli has also pointed out the nature of the mistake made by 

 earlier experimentalists : they had identified a new generation that 

 had developed from eggs as the old generation again risen from the 

 dead. It was found necessary always to dry the Rotifers on sand, 

 preferably that from the tank in which the Rotifers grew. Dr. 

 Faggioli has shown that the eggs are not destroyed by drying, and 

 that when the experiments were successful, eggs must have been 

 introduced with the sand or in the bodies of the Rotifers. On placing 

 these eggs in suitable conditions development proceeds, and a new 

 crop of Rotifers is the result. 



There can be no doubt that the supposed recovery of the 

 Water-Bears (Tardigrada) affirmed by Doyere, admits of the same 

 simple explanation. 



Another oft-quoted marvel that has recently been further exposed 

 is the wonderful adaptability of the freshwater Polype, Hydra. It 

 has long been said that if Hydra be turned inside out it accepts the 

 situation, and lets its skin act as its stomach, and its stomach as its 

 skin. This and many other antics were observed by Trembley, and 

 described in a memoir issued in 1744 ; they were very widely believed 

 in an age which knew little or nothing about the differences between 

 ectoderm and endoderm, and which never troubled whether the 

 spermatozooids were formed from the former or the latter, and which 

 had never heard of mesoglaea. With the growth of knowledge of 

 Hydroid anatomy, however, the story became discredited, and now 

 some Japanese biologists have repeated the experiment, the results 

 suggesting that Hydras have changed their habits rather than their 

 skins, or that the worthy Abbe's observations were not as careful as 

 they might have been. The Hydras may live for a little time under 



1 " De la pretendue reviviscence des Rotiferes, " Archiv. ital. Biol., vol. xvi., 

 pp. 360-374 (1891). 



