X CALIFORNIA ACADEMY OF SCIENCES. 



ISOLATION AS A FACTOR IN THE EVOLUTION OF SPECIES. 110 



PHYSIOLOGICAL SELECTION 110 



Romanes' three difficulties in natural selection considered as a 

 theory of the origin of species, 110; explanation of physiological 

 selection, 111; sterility of species, 111; variations in the repro- 

 ductive system as correlated with other variations, 113; on the 

 swamping effects of interbreeding and the inutility of specific 

 characters, 114; objections to physiological selection by Meldola 

 and Galton, 115; Romanes' reply to these objections, 116; Wal- 

 lace's objections, 117; Romanes' reply to Wallace, 118; Seebohm's 

 criticisms, 121; Romanes' answer, 122; Dyer's criticisms, and 

 Romanes' refutation of his objections, 123; conclusions concern- 

 physiological selection, 124. 



GULICK ON ISOLATION. 125 



Resemblance and difference between the view of Romanes and 

 Gulick, 125; criticism of his views, as ignoring the origin of varia- 

 tions, 126; necessity for isolation established, 127; forms of isola- 

 tion, 128 et seq. 



II. THE COLORS OF NORTH AMERICAN 



BIRDS. 



ON MODES OF PLUMAGE CHANGES 132 



By the feather itself becoming altered in color, 133; by the wear- 

 ing off of the lengthened lighter-colored tips of the feather, 135; 

 classification of different modes of plumage change, 137. 



GENERAL PRINCIPLES OF COLOR IN BIRDS 137 



On the physical and mechanical causes of color effects, 137; state- 

 ment of the theory of bird colors to be elaborated, 139; law of as- 

 sortment of pigments, 140; examples illustrating this law, 140; 

 on generalized and specialized colors, 142. 



THE PROPORTION AND DISTRIBUTION OF THE COLORS IN 



NORTH AMERICAN GENERA 143 



On the general distribution of the fundamental colors among 

 North American genera, 143; the bearing of these facts on the law 

 of the assortment of pigments, 145; the proportion and distribu- 

 tion of black, 146; white, 151; black and white as cognate colors, 

 152; the proportion and distribution of red, 153; red and yellow 

 as correlative colors, 154; examples showing this interdependence, 

 155; the proportion and distribution of yellow, 157; blue, 157; 

 generalizations from foregoing facts, 158. 



THE PATTERN OF MARKINGS 159 



ON INDIVIDUAL FEATHERS 159 



Feather markings as affected by the general laws of growth, 159; 

 Eimer and Kerschnef on feather markings, 162; secondary pig- 



