232 INSTINCT : 



Another excellent example of the plasticity of Instinct ; 

 that is, of the way in which an instinct will vary under new 

 conditions, has been recorded by G. J. Romanes. This 

 ingenious observer writes* : — 



"Three years ago I gave a pea-fowl's egg to a Brabma hen to 

 Latch. The hen was an old one, and had previously reared many 

 broods of ordinary chicliens with unnsnal success, even for one of 

 her breed. In order to hatch the pea-chick, she had to sit one 



week longer than is requisite to hatch an ordinary chick 



The object with which I made this experiment, however, was that 

 of ascertaining whether the period of maternal care subsequent to 

 incubation admits, under peculiar conditions, of being prolonged; 

 for a pea-chick requires such care for a very muoh longer time than 

 does an ordinary chick. As the separation between a hen and her 

 chickens always appears to be due to the former driving away the 

 latter when they are old enough to shift for themselves, I scarcely 

 expected the hen in this case to i)rolong her period of maternal care, 

 and, indeed, only tried the experiment because I thought that if 

 she did so, the fact would be the best one imaginable to show in 

 ivhat a high degree heredUary instinct may he modified by peculiar 

 individual experience. The result was very surprising. For the 

 enormous period of eighteen months this old Brahma hen remained 

 with her ever-growing chicken, and throughout the whole of that 

 time she continued to pay it unremitting attention. She never 

 laid any eggs during this lengthened period of maternal supervision, 

 and if at any time she became accidentally separated from her 

 charge, the distress of both mother and chicken was very great. 

 Eventually the sep^aration seemed to take place on the side of the 



peacock In conclusion, I may observe that the peacock 



reared by this Brah ma hen, turned out a finer bird in every way than 

 did any of his brothers of the same brood which were reared by 

 their own mother; but that, on repeating the experiment next 

 year with another Brahma hen and several pea-chickens, the result 

 was different, for the hen deserted her family at the time when il 

 is natural for ordinary hens to do so, and, in consequence, all the 

 pea-chickens miserably perished." 



Another observation proving the modifiability of In* 

 * " Nature," October 25, 1875, p. 553. 



