282 THE PRINCIPLES OF Part II. 



have moulted two, three, or four times ; and these 

 modifications of* plumage are regularly transmitted. 



Inheritance at Corresponding Seasons of the Year. 

 — With animals in a state of nature innumerable 

 instances occur of characters periodically appearing at 

 different seasons. We see this with the horns of the 

 staar, and with the fur of arctic animals which becomes 

 thick and white during the winter. Numerous birds 

 acquire bright colours and other decorations during the 

 breeding-season alone. I can throw but little light on 

 this form of inheritance from fa r tts observed under 

 domestication. Pallas states, 21 that in Siberia domestic 

 cattle and horses periodically become lighter-coloured 

 during the winter ; and I have observed a similar 

 marked change of colour in certain ponies in England. 

 Although I do not know that this tendency to assume a 

 differently coloured coat durinff different seasons of the 

 year is transmitted, yet it probably is so, as all shades of 

 colour are strongly inherited by the horse. Nor is this 

 form of inheritance, as limited by season, more remark- 

 able than inheritance as limited by age or sex. 



Inheritance as Limited hy Sex. — The equal trans- 

 mission of characters to both sexes is the commonest 

 form of inheritance, at least with those animals which 

 do not present strongly -marked sexual differences, and 

 indeed with many of these. But characters are not 

 rarely transferred exclusively to that sex, in which they 

 first appeared. Ample evidence on this head has been 

 advanced in my work on Variation under Domestica- 



21 'Novae species Quadrupedum e Glirium ordine,' 1778, p. 7. On 

 the transmission of colour by the horse, see ' Variation of Animals, &c. 

 under Domestication/ vol. i. p. 21. Also vol. ii. p. 71, for a general 

 discussion on Inheritance as limited by Sex. 



