BLENDED ORIGIN, OR PLASTICITY OF INSTINCT. 213 



" Spanisli hens, as is notorious, scarcely ever sit at all ; but 

 I have one purely bred one just now that sat on dummies for 

 three days, after which time her patience became exhausted. 

 However, she seemed to think that the self-sacrifice she had 

 undergone during those three days merited some reward, for 

 on leaving tlie nest, she turned foster-mother to all the 

 Spanish chickens in the yard. They were sixteen in number, 

 of all ages, from that at which their own mothers had just 

 left them up to full-grown chickens. It is remarkable, too, 

 that although there were Brahma and Hamburg chickens in 

 the yard, the Spanish hen only adopted those of her own 

 breed. It is now four weeks since this adoption took place, 

 but the mother as yet shows no signs of wishing to cast oft' 

 her heterogeneous brood, notwithstanding that some of her 

 adopted chickens have grown nearly as large as herself. 



" The following, however, is a better example of what may 

 be called plasticity of instinct. Three years ago I gave a pea- 

 fowl's e<y^ to a Brahma hen to hatch. The hen was an old one, 

 and had previously reared many broods of ordinary chickens 

 with unusual 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, but in this there is nothing 

 very unusual, for, as Mr. Spalding observes, the same thing 

 happens with every hen that hatches out a brood of ducklings.* 

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

 that of ascertaining whether the period of maternal care sub- 

 sequent to incubation admits, under pecuKar conditions, of 



unsatisfied, induces even sucli an intelligent animal as man to adopt progeny ; 

 and the proverbial passion of old maids for keeping cats, dogs, and other 

 domestic animals, is probably analogous to the cases given in the text of 

 female animals adopting the young of other species. 



In this connection I may quote the following account which I have 

 received from a friend, whom I know to be an accui'ate and conscientious 

 observer ; for it shows that even among birds in a state of nature the yearn- 

 ing for progeny may induce them to adopt the young of other species, just as 

 in the cases of birds in a state of domestication which are about to be given 

 in the text: — 



" In July, 1878, I found a wren's nest A^-ith young birds, which were being 

 fed by a wren and a sparrow. I made sure that the young birds were wrens, 

 and 1 noticed that the sparrow continued to feed them after they had left the 

 nest. The behaviour of the two birds was very dissimilar, the vrren being 

 bold and its visits to the nest incessant, whereas the sparrow was very shy and 

 its visits much less frequent." 



* The greatest prolongation of the incubatory period I have ever known 

 was in the case of a pea-hen, which sat very steadily on addled eggs for a 

 period of four months, and had then to be forced off in order to save hei- life. 



