550 THE WONDER OF LIFE 



reflect the light like mirrors and are effective guide-marks. 

 Attractive Coloration. A fifth use of coloration 

 is to add to the cn&mble of attractiveness which one sex 

 has for the other, and which, by stimulating sexual interest 

 and increasing sexual excitement, makes pairing more effec- 

 tive. It is usually the male who is the more decorative and 

 brilliant, but there are exceptional cases of the reverse. 

 The tail of the peacock is a masterpiece in this kind of 

 coloration, and the decora tiven ess of male Birds of Para- 

 dise- and Lyre-Birds and Pheasants is hardly less transcen- 

 dent. The habits of Bower-birds and some other birds 

 .1 .siuolco fcighd Hriw slsopifl^, afifiMft , J 

 ./ieihalS . . nolirO .muilBinsQ JlaHS jJeuT 

 .<! ^.ladfriJJDuD B32 .I 1 .(.giwtuJ tsi\K) .atrtieoqae laleBni 



sthetic 



.:< -. . beauty, vigour and 



other qualities fire of sexual 



excitement in the coy femuk:-. 



The brilliant coloration o sure 



latent in the females, as is shown in cases where an old 

 female bird, or one with an abnormal ovary, begins to put 

 on a masculine dress. The masculine characteristics are, 

 as it were, seeds which will not normally develop except 

 in male soil. They are parts of the inheritance, but they 

 do not start developing except in appropriate soil aji 

 response to appropriate stimulus. It has been sh 

 experimentally that the stimulus, in some cases at 1- 

 is furnished by the ' hormones ' or internal secretions o 

 reproductive organs which are diffused by the blcxx ; 

 out the body when the organism becomes adoleso* 

 when the breeding season sets in. It is int;-- 



