156 READINGS IN BIOLOGICAL SCIENCE 



sexually, but that here the sexual and asexual methods of reproduction 

 alternate in a peculiar way. The green mosses form eggs and sperms, but 

 the fertilized egg does not develop into another moss plant. It forms a 

 capsule on a brown stalk, in which asexual spores are formed. These fall 

 to the ground and eventually germinate to form a new sexual plant. Thus 

 the little moss plant has two life periods: in the first it lives as a green plant, 

 which forms sexual organs; in the second as a brown capsule, which forms 

 asexual spores. 



The ferns, horsetails, and lycopods all go through these two phases, 

 though in them the sexual individuals are small and inconspicuous, while 

 the asexual, on the other hand, are large, being (in the case of ferns) the 

 actual fern plants, which bear asexual spores. Among flowering plants, 

 the first, or sexual phase, is very much reduced. While the algae repro- 

 duce themselves now sexually, now asexually, the higher plants, from the 

 mosses upwards, follow an ordered alternation of the two methods of 

 reproduction; the higher the plant, the more developed is its asexual phase, 

 and the more reduced the sexual phase becomes. The meaning of this al- 

 ternation is by no means clear. 



More recently the analysis of the behavior of the chromosomes during 

 fertilization has shown that there are specific sex-determining chromo- 

 somes; further, that the inheritance of sex follows the same Mendelian 

 rules as does the inheritance of any other bodily character. This does 

 nothing, however, to help in the understanding of the whole phenomenon 

 of sex. 



2. THEORIES ABOUT THE NATURE OF SEX 



The philosophy of sex, to which man has always devoted much thought, 

 has passed to-day into the chromosome theory. Much of Aristotle's philo- 

 sophical system originated in the recognition of the difference between 

 the two sexes; this gave him his ideas about matter and form. In the fe- 

 male are embodied the passive principles, in the male the active, creative, 

 formative principles. Even Harvey allowed himself to be influenced bv 

 these ideas, and he compared the female uterus with the brain; as the latter 

 possesses the power to form images of external objects, so the uterus — 

 whose ideas are the eggs — forms them in the image of the fertilizing male. 

 In the speculations of the evolutionists of the eighteenth century the 

 broader aspects of sex were absolutely neglected. The result of the dis- 

 covery of eggs and spermatozoa was that the true nature of the problem 

 was obscured. They imagined that they could answer all questions on the 

 subject by examining those structures. The theory that the complete 

 man Hes already enclosed within the ovum or the spermatozoon suggested 

 that one sex, either the male or the female, represented a superfluous, pur- 

 poseless creation of mother nature. 



The German romantic philosophers looked with wonder upon the 



