44 



Panmixia, or the cessation of selection, Romanes, 

 Weismann. 



The reduction from survival mean to birth 

 mean. 



Economy of growth and reversed selection, Darwin. 



Loss of carapace in parasitic barnacles. 



Loss of wings in insular insects. 

 Difficulty as to the final disappearance of organs. 



Reversed selection, Panmixia, Weismann. 



Failure of heredity, Romanes. 



Germinal selection, Weismann. 



v. Sexual Selection. 



(Darwin, The Descent of Man, Vol. i, pp. 245-409, and Vol. 

 2, pp. 1-387 ; Wallace, Natural Selection and Tropical Na- 

 ture, pp. 338-394; Wallace, Darwinism, pp. 268-300; Ro- 

 manes, Darwin and after Darwin, Vol. i, pp. 284-335 ! Lloyd 

 Morgan, Animal Life and Intelligence, pp. 197-209; Brehm, 

 North Pole to Equator.) 



a. The law of battle. 



b. The aesthetic sense of birds. 



c. Courtship. 



Among birds. 

 Among spiders. 



d. Ornamental secondary sexual characters developed 

 by sexual selection. 



e. Evidence. 



(1) These characters are confined to the sex that 



is active in courtship, almost always the 

 male. 



(2) They are as a rule developed only at matur- 



ity and often only during the breeding 

 season. 



