2 12 THE PROTOZOA 



in volume continually tends to outrun that of surface, for the former 

 increases as the cube of the diameter, the latter only as the square. 

 The mass of living protoplasm must, therefore, increase more rapidly 

 than the surface which serves to keep it alive, and the isolated cell 

 tends to come first to a physiological standstill, and second to a period 

 of decline, since the surface of nutrition, respiration, and excretion is 

 incommensurate with the bulk of protoplasm. Cell-division, there- 

 fore, which Spencer characterized as an indication of the limit of 

 growth, becomes an apparent necessity. 



Growth, or the preponderance of constructive processes, leads thus 

 indirectly to increase of surface by division of the cell, but in conju- 

 gation or fertilization the very opposite phenomenon occurs, viz. the 

 increase in bulk of the cell with a consequent relative decrease in sur- 

 face because of the union of two cells. Geddes and Thompson ('90), 

 like Spencer, emphasize the connection between division and the 

 advent of preponderating katabolism within the cells, and in their 

 interesting work on the Evolution of Sex, interpret male and female 

 organisms in terms of relative metabolism, the male being regarded as 

 relatively katabolic, the female as anabolic. These authors interpret 

 fertilization as a " katabolic stimulus to an anabolic cell, and on the 

 other side, of course, as an anabolic renewal to a katabolic cell, as well 

 as the union of opposed hereditary characteristics." x 



If, as Minot ('79) suggested, every newly formed organism be re- 

 garded as having a certain initial potential energy which is gradually 

 used up in its life-activities to be restored by conjugation, then the 

 union of two cells may be interpreted as a renewal of vigor or a " re- 

 juvenescence " (Maupas), a view of fertilization first expressed by 

 Butschli ('76), Engelmann {'76), and Minot ('77, '79), and apparently 

 confirmed later by Maupas ('88, '89) through his admirable observa- 

 tions on the life-cycle of Infusoria. O. Hertwig ('76) also, in con- 

 nection with fertilization of the metazoan egg, arrived at a similar 

 dynamic view of fertilization, maintaining that protoplasm gradually 

 tends toward a state of stable equilibrium expressed by decreased 

 activity, etc., and that it is restored to a more unstable or more labile 

 condition by conjugation or fertilization. The force of these views 

 as to the need of conjugation for different species of Infusoria, at 

 least, can hardly be questioned ; for, as repeatedly stated in the pre- 

 ceding chapters, reproduction by simple division may go on for a 

 certain number of generations, but cannot continue indefinitely, unless 

 at certain intervals, which Maupas has shown to be more or less 

 definite, two individuals unite in conjugation. This union, in some 

 wholly unexplained way, imparts to each of the conjugants 



1 Loc. a'/., p. 252. 



