male and female traits (from Hermes and Aphrodite). In common earthworms, 

 for example, each individual bears both ovaries and spermaries. But no in- 

 dividual fertilizes its eggs with its own sperms. There is an exchange of seminal 

 fluid between two individuals, and the eggs of each are fertilized by sperms 

 received from the other. 



The common oyster of the northern Atlantic coast is interesting in this 

 connection, since each individual is both male and female — but not at any one 

 time. A female oyster will produce a large number of eggs, which are dis- 

 charged into the water, where they are fertilized by sperms from other in- 

 dividuals. After a time, the ovaries become inactive and spermaries develop. 

 Each individual periodically reverses its sex. 



Primary Sex Characters In countless varieties of plants and animals 

 reproduction consists only in the fusing of two unspecialized cells into a 

 zygote. Biologists have therefore come to apply the terms male and female 

 primarily to the gametes and to the special organs that produce these special- 

 ized reproductive cells. A male individual is thus one that bears sperms; a 

 female, one that bears eggs. 



Maleness and femaleness were generally taken for granted in familiar ani- 

 mals, but in ancient times it was commonly believed that there could be no 

 sex in plants. Farmers and gardeners and fruit-raisers, however, knew from 

 very ancient times that it is the flower of the common plants that produces 

 the fruit and seed. They knew also that merely bearing flowers and having 



MALE AND FEMALE GERM CELLS 



The female gamete is usually spherical and inert, or passive, containing a great deal 

 of nutrient material in proportion to its living protoplasm. The diameter of the human 

 egg is about four times the length of the sperm, which means that it is many thousand 

 times as large in volume. Sperm cells are typically ciliated or flagellated, and they 

 swim rapidly in all directions 



388 



