Maech 8, 1907] 



SCIENCE 



373 



the union of particular cellular individuals, 

 has in it none of the obviousness of the 

 individual's preservation by the taking of 

 food. 



The nature of the periodic need for 

 fertilization has been differently conceived 

 by different writers. Weismann believes 

 that fertilization-need has arisen in the 

 course of evolution in order to ensure the 

 advantages of amphimixis to the race; it 

 has no fundamental physiological basis. 

 R. Hertwig propounds the hypothesis that 

 there is an innate tendency to acceleration 

 of the vital processes, due to the gradual 

 adaptation of nucleus and cytoplasm in 

 their copartnership, which proves gradu- 

 ally harmful and ultimately fatal. Fertil- 

 ization checks the acceleration by intro- 

 ducing a foreign nucleus, unaccustomed to 

 the protoplasmic milieu ; but the new part- 

 ners in the vital process gradually accel- 

 erate the speed until a second fertilization 

 again checks the dangerous pace. Fertil- 

 ization thus marks the return to a state of 

 stability from a state of extreme cellular 

 lability. Herbert Spencer, on the other 

 hand, regards the vital processes as tending 

 towards a state of equilibrium or fixed 

 stability; fertilization restores the labile 

 condition of the cell. According to Geddes 

 and Thompson, fertilization may be com- 

 pared to mutual digestion and may have 

 arisen from a nutritive want. "With the 

 differentiation of the elements on anabolic 

 and katabolic lines, the nature of the fer- 

 tilizing act becomes more definite. * * * 

 The union of the two sets of products re- 

 stores the normal balance and rhythm of 

 cellular life." 



The point of view that has been, perhaps, 

 the most acceptable to zoologists was stated 

 originally by Biitschli, Engehnann, Minot 

 and Maupas, and was based primarily on 

 the study of conjugation in infusoria. It 

 was discovered that, during the series of 

 asexual generations, there is a gradual 



diminution of vitality expressed in a re- 

 duced rate of division and in certain mor- 

 phological changes that may be collectively 

 designated senescent. Conjugation changes 

 all this; senile processes cease, the division 

 rate is restored. Thus conjugation ap- 

 parently reverses the process of senescence, 

 causes rejuvenescence. By an extension 

 of this idea it was assumed that in Metazoa 

 the fertilized ovum starts out charged with 

 abundant vitality, which is, however, grad- 

 ually exhausted, and the race is saved only 

 by fertilization, which is here also inter- 

 preted, by a reckless transfer of terms, as 

 rejuvenescence. 



The majority of zoologists appear to be 

 agreed that fertilization-need is a pri- 

 mordial physiological condition, more than 

 a mere adaptation to ensure amphimixis; 

 and though there are weighty authorities 

 on the other side, this point of view ap- 

 pears to me to be right, even though the 

 theories of the nature of the need and its 

 satisfaction are inconsistent. The idea of 

 Spencer is too indefinite to serve either for 

 foundation of a more extensive theory, or 

 as basis for observation and experiment. 

 That of R. Hertwig is in opposition to so 

 many known facts as to be untenable. The 

 conception of rejuvenescence has a flavor 

 of mysticism, and involves a confusion of 

 ideas. It implies that the gametes are 

 senescent before fertilization, but the only 

 significance of the term senescent is in its 

 application to the soma. That the germ- 

 cells before fertilization are old, in the sense 

 that tissue-cells become old, would be as- 

 serted by no one. They are, on the con- 

 trary, the spring of eternal youth, and all 

 that can be asserted objectively is the neces- 

 sity of fertilization for their continual 

 functioning. 



Even in the case of Protozoa there is no 

 reason for assuming that the part prin- 

 cipally concerned in conjugation, the 

 nucleus, is itself old; the cell-body uk- 



