II2 THE EVOLUTION OF SEX. 



not know why or how sexual individuals are produced." In regard 

 to the sex-elements, we have already noticed his opinion that they are 

 at first "hermaphroditic or asexual," and that both differentiate by 

 the extrusion or separation of the contradictory elements, the ovum 

 getting rid of male polar globules, the sperms leaving behind a female 

 mother-cell remnant. 



Brooks has emphasized rather a different aspect of the question. 

 ' ' A division of physiological labor has arisen during the evolution of 

 life, the functions of the reproductive elements have become specialized 

 in different directions. " " The male cell became adapted for storing 

 up gemmules, and, at the same time, gradually lost its unnecessary 

 and useless power to transmit hereditary characteristics." "The 

 males are, as a rule, more variable than the females; the male leads, 

 and the female follows, in the evolution of new races." Brooks does 

 not exactly attack the problem of the nature and origin of sex, but 

 his emphasis on the greater variability of males is of much importance. 



These three positions must be taken as representative; others 

 which appeal to superiorities, polarities, and like mysteries, can hardly 

 claim scientific standing, and have been already sufficiently referred to 

 at p. 28. To those which interpret the sexes in terms of the advan- 

 tages of sexual reproduction, and to those which deal almost exclu- 

 sively with the problem of fertilization, we shall afterwards return. 

 The truth, in fact, is, that it is difficult to find any answer at once 

 serious and direct to the question of the fundamental difference between 

 male and female. 



II. Nature of Sex as seen in the Sex-elements. — The Cell- 

 cycle. — As ova and sperms are the characteristic products of female 

 and male organisms, it is reasonable that an interpretation of sex should 

 start at this level. Here, assuredly, the difference between male and 

 female has its fundamental and most concentrated expression. For 

 the bodies, after all, as Weismann has so clearly emphasized, are but 

 appendages to this immortal chain of sex-cells. 



We have already pointed out that the sex-cells are more or less 

 on a level with the Protozoa. If we only knew, they probably differ 

 widely from them in those intricacies of nuclear structure of which we 

 only see the surface; yet as single cells the sex-cells are comparable 

 with the Protozoa. For the moment, let us study those simplest 

 organisms. Even a student, shown an extended series of unicellular 

 forms, amoebae, foraminifers, sun-animalcules, infusorians, gregarines, 

 and some of the simplest algae as well, might gradually begin to 

 group these in his mind under three divisions. First there are highly 

 active cells, — infusorians of all sorts; at the opposite extreme there 



