Chap. XXV. CORRELATED VARIABILITY. 329 



Here is a more curious case : white cats, if they have blue 

 eyes, are almost always deaf. I formerly thought that the rule 

 was invariable, but I have heard of a few authentic exceptions. 

 The first two notices were published in 1829, and relate to 

 English and Persian cats : of the latter, the Eev. W. T. Bree 

 possessed a female, and he states " that of the offspring pro- 

 " duced at one and the same birth, such as, like the mother, 

 " were entirely white (with blue eyes) were, like her, invariably 

 "deaf; while those that had the least speck of colour on their 

 " fur, as invariably possessed the usual faculty of hearing." 21 

 The Eev. W. Darwin Fox informs me that he has seen more 

 than a dozen instances of this correlation in English, Persian, 

 and Danish cats; but he adds "that, if one eye, as I have 

 " several times observed, be not blue, the cat hears. On the 

 " other hand, I have never seen a white cat with eyes of the com- 

 " mon colour that was deaf." In France Dr. Sichel 22 has ob- 

 served daring twenty years similar facts ; he adds the remark- 

 able case of the iris beginning, at the end of four months, to 

 grow dark-coloured, and then the cat first began to hear. 



This case of correlation in cats has struck many persons as 

 marvellous. There is nothing unusual in the relation between 

 blue eyes and white fur; and we have already seen that the 

 organs of sight and hearing are often simultaneously affected. 

 In the present instance the cause probably lies in a slight arrest 

 of development in the nervous system in connection with the 

 sense-organs. Kittens during the first nine days, whilst their 

 eyes are closed, appear to be completely deaf; I have made a 

 great clanging noise with a poker and shovel close to their heads, 

 both when they were asleep and awake, without producing any 

 effect. The trial must not be made by shouting close to their ears, 

 for they are, even when asleep, extremely sensitive to a breath 

 of air. Now, as long as the eyes continue closed, the iris is no 

 doubt blue, for in all the kittens which I have seen this colour 

 remains for some time after the eyelids open. Hence, if we sup- 

 pose the development of the organs of sight and hearing to be 

 arrested at the stage of the closed eyelids, the eyes would re- 



21 Loudon's ' Mag. of Nat. Hist.,' vol. on the inheritance of deafness in cats, 

 i., 1829, pp. 66, 178. See also Dr. P. 22 « Annates des Sc. Nat.' Zoolog., 3rd 



Lucas, ' L'Hered. Nat.,' torn. i. p. 428, series, 1847, torn. viii. p. 239. 



