I5 2 THE EVOLUTION OF SEX. 



in chemical terms. But a due impression of the marvelous "individuality " of 

 the nuclear elements may be combined with a general physiological interpreta- 

 tion of the entire process. 



It has been already noted, in regard to the origin of fertilization 

 that the almost mechanical flowing together of exhausted cells is 

 connected by the stages of multiple conjugation with the ordinary 

 form of the latter, while the respective differentiation of the two 

 elements effects the transition to fertilization proper. Historically, 

 then, fertilization is comparable to mutual digestion, and, though 

 bound up with reproduction, has arisen from a nutritive want. With 

 the differentiation of the elements on anabolic and katabolic lines, the 

 nature of the fertilizing act becomes more definite. The essentially 

 katabolic male cell, getting rid of all accessory nutritive material 

 contained in the sperm-cap and the like, brings to the ovum a supply 

 of characteristic waste products or katastates, which stimulate the 

 latter to division. The profound chemical differences surmised by 

 some are intelligible as the outcome of the predominant anabolism and 

 katabolism in the two elements. The union of the two sets of 

 products restores the normal balance and rhythm of cellular life. 

 Rolph's suggestion is thus included and defined. 



IV. Use of Fertilization to the Species. — Not a few natural- 

 ists have passed from the individual aspect of fertilization to its general 

 import in relation to the life of the species. Why should fertilization 

 occur at all, if parthenogenesis in some cases works so well ? Part of 

 this question is almost illegitimate, if the existence of male and female 

 be, as we think, simply the expression of a more developed swing of 

 "the organic seesaw" between anabolism and katabolism. The 

 answers have, however, much interest, and are valuable, so long as 

 they are not magnified so as to hide the deeper physiological problems 

 lying below. The origin and physiological import of fertilization can 

 never be explained by any elucidation of its subsequent advantageous- 

 ness. 



The two naturalists who have recently reached the most valuable 

 results in regard to the uses of fertilization are Maupas andWeismann. 

 This they have done by very different paths, — Maupas, in working 

 out the details of conjugation in infusorians; Weismann, in his wider 

 studies on the problems of heredity and evolution. To Maupas, fertili- 

 zation is necessary to prevent the death of the species; to Weismann, 

 fertilization is the ever recurrent beginning of new vital changes, and 

 the continual preservation at the same time of the relative constancy 

 of the species. Several naturalists of the highest reputation have 

 regarded fertilization as a process which supplied a fresh life-impulse 

 to the species. Thus Galton has insisted, with much clearness and 



