206 THE VARIATION OF ANIMALS IN NATURE 



(12) Davenport (1908) : attacks on poultry by crows. 



The author observed the attacks by crows on 300 chicks 

 in a poultry run. Of 300 chicks 24 were killed. The 

 constitution of the original 300 was as follows : 



40 per cent, white. 

 40 „ „ black. 

 20 „ „ more or less like the Jungle Fowl ( c pencilled '). 



If there had been no selection, the expectation would be 

 that of the 24 killed, 9-6 would be white, 9-6 black and 4-8 

 ' pencilled.' 



Actually of the killed, 10 were white, 13 black, and 1 was 

 ' grey and buff.' No pencilled birds were killed. 



Davenport assumes that the inconspicuous ' pencilled ' 

 type is preserved by its colour. 



We think that the extremely low total of 24 birds is quite 

 inadequate as a basis of estimating the effects of selection. 

 It seems to us extremely problematical whether the ' pencilled ' 

 birds are in fact less conspicuous than the white and black. 



(13) Crampton (1904) : death-rate of the pupa of a Saturniid Moth. 



Crampton, observing that numerous cocoons of Philosamia 

 cynthia contained dead individuals, attempted to discover the 

 causes of pupal and imaginal elimination. He obtained from 

 trees 1,090 cocoons, of which 55 had not pupated and 93 had 

 left the pupal case. Of the remaining 942 pupae, 623 had 

 pupated, but were dead. Only 319 'selected' individuals 

 were alive. 



Equal numbers of dead and survivors were measured for 

 length of antenna and various proportions of the ' bust.' The 

 survivors were kept till the metamorphosis was over. 



(i) Pupal stage. — Estimates were made for ' type ' (i.e. 

 the average sizes and proportions) and ' variability ' 

 in 8 characters. When the measurements of dead 

 and survivors (6*) were statistically compared, it 

 was found that the differences suggested that selection 

 must have occurred in 5/8 characters, that it was 

 probable in 2/8 and possible in 1/8. Where the 

 variability was compared, the survivors were less 

 variable in 1 /8 cases, possibly so in another, and not 



