Il8 LIFE AND DEATH. [III. 



When in this case the specific organization degenerates 

 to a certain extent, such changes depend in part upon the 

 endeavour to diminish as far as possible the size of the or- 

 ganism—the pseudopodia being drawn in, while the vacuoles 

 contract and completely disappear. The degeneration maj' 

 also, perhaps, depend in part upon the secretion of the C3'st 

 itself, which implies a certain loss of substance '. But de- 

 generation chiefly depends upon the fact that the encystment 

 is accompanied by reproduction in the way of fission, which 

 seems to begin with a simplification of the organization, that 

 is, with a fusion of the numerous nuclei. It is well known 

 that many unicellular animals contain several nuclei — in other 

 words, that the nuclear substance is scattered in small parts 

 throughout the whole cell. But when the animal prepares 

 for division, these pieces of nuclear substance fuse into a 

 single nucleus which itself undergoes division into two equal 



in all essentials with that expressed above. Biitschli saj's (Bronn's 

 ' Klassen und Ordnungcn dcs Thierreichs,' Protozoa, p. 148): 'The 

 process of encj'stment does not appear to have originally borne any 

 direct relation to reproduction : it appears on the contrary to have 

 taken place originall}', — as it frequently does at the present day, — either 

 for the protection of the organism against injurious external influences, 

 such as desiccation 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 Tetat de vie active, sc 

 reproduisent dans une sorte d'etat de repos, dit etat d'enk^-stement. 

 Ces sortes de kystes peuvent ctrc designes sous le nom de kystes de 

 reproduction, par opposition avec d'autres kj'stes, dans lesquels les 

 Inl'usoires se renferment pour se soustraire a des conditions devenues 

 defavorables du milieu qu'ils habitcnt, le manque d'air, le dessechement, 

 etc. — ceux-ci sont dcs kystes de conservation . . .' 



' This is of importance in so far as single individuals might be thus 

 compelled to encyst even when the existing external conditions of life 

 do not require it. The substance which Actinosphaeriunt, for example, 

 employs in the secretion of its thick siliceous cyst must have been 

 gradually accumulated by means of a process peculiar to the species. 

 We can scarcely be in error if we assume that the silica accumulated 

 in the organism cannot increase to an unlimited extent without injury 

 to the other vital processes and that the secretion of the cyst must 

 take place as soon as the accumulation has exceeded a certain limit. 

 Thus we can understand that encystment may occur without any ex- 

 ternal necessity. Similarly', certain Entomostraca (e.g. Mohta produce 

 winter-eggs in a particular generation, and these are formed even 

 when the animals are kept in a room protected from cold and desic- 

 cation. 



