LECTURE X. 



THE MEANING OF SEX. 



"Whatever is desirable becomes necessary as soon 

 as it is possible." Law of natural selection. Division 

 of labor in organs and organisms. Division of labor 

 between sexes. Neither sex superior nor prior to 

 other. Mutual help involves mutual dependence. 

 Specialization involves helplessness. Progress implies 

 certain degradation of non-specialized structures. 

 Law of "Compensation." 



Egg-bearing creatures less active than those not so 

 burdened. Activity co-ordinated with strength. Co- 

 ordination of sensorium, brain, and motion. 



Progress of Evolution makes embryo more and more 

 important ; the waste less and less. 



Retention of eggs saves them from early destruction 

 and lessens their number ; saving of eggs through 

 fertilization before extrusion ; by viviparity ; by nour- 

 ishment by milk ; by care for young. Destruction of 

 Saurians, who did not care for the young. Viviparity, 

 and lactation, and care make a birth important. 

 u But one young one at a birth ; but that was a lion." 



Saving with plants through flowers and insect help. 

 Petals are leaves modified to call insects. One of 

 Nature's advertisements. Winds and pines. Waste 

 of pollen. 



Parents differentiated as protectors of young. Give 



