LIFE AND DEATH. 117 



encystment, rejuvenescence can only be understood in the sense in 

 which we speak of the fable of the Phoenix, which, when old, was 

 believed to be consumed by fire, and to rise again from its own 

 ashes as a young- bird. I doubt whether this idea is in agreement 

 with the physiology of to-day, or with the laws of the conservation 

 of energy. It is easy to pull down an old house with rotten beams 

 and crumbling walls, but it would be impossible to build it anew 

 with the old material, even if we used new mortar, represented in 

 Gotte's hypothesis by water and oxygen. For these reasons I con- 

 sider the idea of rejuvenescence of the encysted individual to be 

 contrary to pur present physiological knowledge. 



It is much more simple and natural to regard encystment as 

 adapted for the protection of certain individuals in a colony from 

 destruction by being dried up or frozen, or for the protection of the 

 individual during multiplication by division, when it is helpless, 

 and would easily fall a prey to enemies, or to secure advantages in 

 some other way 1 . The case of Actinospkaerium, mentioned by 

 Gotte, clearly demonstrates that rejuvenescence of the individual is 

 not the only event which happens during encystment, for this 

 would scarcely require six months. The long duration of latent 

 life, from summer to the next spring, clearly proves that encystment 

 is of the highest importance for the species, in order to maintain the 

 life of the individual through the dangers of an unfavourable season 2 . 



1 Professor Gruber informs me that among the Infusoria of the harbour of 

 Genoa, he has observed a species which encysts upon one of the free-swimming 

 Copepoda. He has often found as many as ten cysts upon one of these Copepods, 

 and has observed the escape of their contents whenever the water under the cover- 

 glass began to putrefy. Here advantage is probably gained in the rapid transport of 

 the cyst by the Crustacean. 



2 The views of most biologists who have worked at this subject agree in all 

 essentials with that expressed above. Butschli says (Bronn's ' Klassen und Ordnungen 

 des Thierreichs,' Protozoa, p. 148) : 'The process of encystment does not appear to 

 have originally borne any direct relation to reproduction : it appears on the contrary 

 to have taken place originally, as it frequently does at the present day, either for 

 the protection of the organism against injurious external influences, such as desicca- 

 tion or the fatal effects of impure water, etc. ; and also to enable the organism, 

 after taking up an unusually abundant supply of food, to assimilate it in safety.' 

 Balbiani (' Journ. de Micrographie,' Tom. V. 1881, p. 293) says in reference to the 

 Infusoria, ' Un petit nombre d'especes, au lieu de se multiplier a 1'etat de vie active, 

 se reproduisent dans une sorte d'etat de repos, dit etat d'enkystement. Ces sortes 

 de kystes peuvent etre designes sous le nom de kystes de reproduction, par opposition 

 avec d'autres kystes, dans lesquels les Infusoires se renferment pour se soustraire a 

 des conditions devenues defavorables du milieu qu'ils habitent, le manque d'air, le 

 dessechement, etc. ceux-ci sont des kystes de conservation . . .' 



