156 THE PROTOZOA 



it can hardly be supposed that the time-factor alone can account 

 for the exhaustion or depression of the vital faculties. It is gener- 

 ally admitted that unicellular organisms, such as the Protozoa, 

 tend, after a greater or less number of generations, to exhibit a 

 certain degree of exhaustion in their vital properties, or, it may be, 

 of derangement in their organization and vital mechanisms. Hert- 

 wig (164) is of opinion that " the conditions of death exist in the 

 living substance from the beginning, and are a necessary conse- 

 quence of its vital function " a generalization which may be 

 accepted for those Protista in which the body exhibits the degree of 

 specialization and structural complication proper to a true cell 

 (as the term is understood in this book see p. 98) ; but it is very 

 doubtful if it is tiue also for the simplest forms of life, such as the 

 bacteria and allied organisms. If it be further admitted that 

 syngamy is the natural remedy in unicellular organisms for a natural 

 disease, the problem before us is to discover, if possible, the precise 

 nature of the derangements, and of the method by which the 

 remedy restores them to the normal functional condition. 



At the outset, attention must be drawn to a very constant and 

 general preliminary to syngamy in Protozoa namely, the elimina- 

 tion of a large amount of chromatin which appears to have been 

 regulating the vital activities during previous generations (vegeta- 

 tive chromatin) , and its replacement by chromatin which has been 

 inactive and lying in reserve (generative chromatin). This process 

 is seen in its most striking form in the Ciliata, where the macro- 

 nucleus is entirely eliminated during the act of syngamy, and is 

 replaced in subsequent generations by a new macronucleus derived 

 from the micronucleus formed by fusion of portions of the micro- 

 nuclei of the partners in syngamy. Hence it might seem as 

 if the chief result of syngamy was to replace effete vegetative 

 chromatin by fresh generative substance which through inactivity 

 has retained its powers unimpaired. But in the first place it must 

 be pointed out that, to effect a replacement of this kind, the union 

 of two individuals is not necessary ; it would be sufficient for a 

 single individual to form a new nucleus from its store of generative 

 chromatin, and to get rid of its old, effete vegetative chromatin. 

 If we regard the chromidia of Arcella as composed of generative 

 chromatin, the buds produced by formation of secondary nuclei 

 from the chromidia would represent nuclear regeneration of this 

 kind. Secondly, it is open to doubt how far the theory of vegeta- 

 tive and generative chromatin can be applied throughout the whole 

 series. In such forms as Arcella the chromidial mass, although it 

 furnishes the gamete-nuclei, is a cell-element in a functional con- 

 dition, and in the more primitive forms the distinction between 

 vegetative and generative chromatin cannot be pressed so far as 



