216 SEXUAL selection: birds. PartIL 



beauty during many years after they are fully mature ; 

 this is the case with the train of the peacock, and with 

 the crest and plumes of certain herons ; for instance, the 

 Ardea Ludovicana ;^^ but it is very doubtful wliether 

 the continued development of such feathers is the 

 result of the selection of successive beneficial variations, 

 or merely of continuous growth. Most fishes continue 

 increasing in size, as long as they are in good health 

 and have plenty of food ; and a somewhat simihxr law 

 may prevail with the plumes of birds. 



Class V. When the adults of both sexes have a dis- 

 tinct winter and summer jplumage, whether or not the male 

 differs from the female, the young resemhle the adults of 

 hoth sexes in their winter dress, or much more rarely in 

 their summer dress, or they resemhle the females alone ; 

 or the young may have an intermediate character; or 

 again, they may differ greatly from the adtdts in hoth 

 their seasonal j^lumages. — The cases in this class are 

 singularly complex ; nor is this surprising, as they 

 depend on inheritance, limited in a greater or less 

 degree in three different ways, namely by sex, age, 

 and the season of the year. In some cases the indi- 

 viduals of the same species pass through at least five 

 distinct states of plumage. With the species, in which 

 the male differs from the female during the summer 

 season alone, or, which is rarer, during both seasons,^^ 

 the young generally resemble the females, — as with 

 the so-called goldfinch of North America, and appa- 

 rently with the splendid Maluri of Australia.*^ AVith 



•*o Jerdon, ' Birds of India,' vol. iii. p. 507, on the peacock. Audu- 

 bon, ibid. voL iii. p. 139, on the Ardea. 



■*^ For illustrative cases see vol. iv. of JMacgillivray's ' Hist. Brit. 

 Birds;' on Triiiga, &c., p. 229, 271; on the Machetes, p. 172; on the 

 Clifiradrius liiatioila, p. 118; on the Cliaradrius plnvialls, p. 94. 



•*2 For the goldfinch of N. America, Fringilla tristis, Liiin., see 



