The Making of Species 



and the golden form of the common carp among 

 captive animals ; and among animals in a state 

 of nature, yellow forms have been recorded of the 

 rose-ringed Paroquet (Palceornis torquatus), the 

 green woodpecker, the pike, and the eel. These 

 lutinistic forms usually have normally coloured 

 eyes. Sometimes, but only very rarely, these 

 yellow forms throw off white sports as, for 

 example, the " silver" form of the goldfish. 

 Finn has seen a white variety of the common 

 carp. White canaries are excessively rare, while 

 white budgerigars are unknown. 



It is worthy of note that entirely yellow species 

 of birds and fish are unknown. We would suggest 

 that the explanation of this is that yellowness is 

 correlated with some physical characteristic un- 

 favourable to an organism exposed to the 

 struggle for existence ; hence individuals which 

 are yellow are not permitted to survive. In some 

 species of moths individuals occur in which the 

 parts normally red are yellow. According to 

 Bateson, a chalk pit at Madingly, near Cam- 

 bridge, has long been known to collectors as a 

 habitat of a yellow-marked form of the six-spot 

 Bur net Moth (Zygczna filipendulcz). These 

 lutinistic forms are not confined to one genus 

 of Butterflies. Moreover, in the Pin-tailed Non- 

 pareil Finch (Eytkrura prasina) of the Eastern 

 Archipelago the red tail and other red parts of 

 the plumage are not infrequently replaced by 



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