ilr8 INHERITANCE. Chap. XIV. 



Dr. P. Liicas has shown "^ tliat when a peculiarity, in no manner 

 connected with the reproductive organs, appears in either parent, 

 it is often transmitted exclusively to the offspring of the same sex, 

 or to a much greater number of them than of the opposite sex. 

 Thus, in the family of Lambert, the horn-like projections on the 

 skin were transmitted from the father to his sons and grandsons 

 alone; so it has been with other cases of ichthyosis, with super- 

 numerary digits, with a deficiency of digits and phalanges, and in a 

 lesser degree with various diseases, especially with colour-blindness 

 and the hsemorrhagic diathesis, that is, an extreme liability to profuse 

 and uncontrollable bleeding from trifling wounds. On the other 

 hand, mothers have transmitted, during several generations, to their 

 daughters alone, supernumerary and deficient digits, colour-blindness 

 and other peculiarities. So that the very same peculiarity may 

 become attaced to either sex, and be long inherited by that sex 

 alone ; but the attachment in certain cases is much more frequent 

 to one than the other sex. The same peculiarities also may be 

 promiscuously transmitted to either sex. Dr. Lucas gives other 

 cases, showing that the male occasionally transmits his peculiarities 

 to his daughters alone, and the mother to her sons alone ; but even 

 in this case we see that inheritance is to a certain extent, though 

 inversely, regulated by sex. Dr. Lucas, after weighing the whole 

 evidence, comes to the conclusion that every peculiarity tends to 

 be transmitted in a greater or lesser degree to that sex in which it 

 first appears. But a more definite rule, as I have elsewhere shown,=^^ 

 generally holds good, namely, that variations which first appear in 

 either sex at a late period of life, when the reproductive functions 

 are active, tend to be developed in that sex alone ; whilst variations 

 which first appear early in life in either sex are commonly trans- 

 mitted to both sexes. I am, however, far from supposing that this 

 is the sole deteiinining cause. 



A few details from the many cases collected by Mr. Sedgwick,^*" 

 may be here given. Colour-blindness, from some unknown cause, 

 shows itself much oftener in males than in females ; in upwards of 

 two hundred cases collected by Mr. Sedgwick, nine-tenths related 

 to men ; but it is eminently liable to be transmitted through women. 

 In the case given by Dr. Earle, members of eight related families 

 were affected during five generations : these families consisted of 

 sixty-one individuals, namely, of thirty-two males, of whom nine- 

 sixteenths were incapable of distinguishing colour, and of twenty- 

 nine females, of whom only one-fifteenth were thus affected. 

 Although colour-blindness thus generally clings to the male sex. 



2^ ' L'Hered. Nat.,* torn. ii. pp. 137- ^^ On Sexual Limitation in Heredi- 



165. /S'^e, also, Mr. Sedgwick's four tary Diseases, ' Biit. an I For. Med. - 



memoii-s, immediately to be referred Chirurg. Review,' April 1861, p. 477 ; 



io. July, p. 198 ; April 1863, p. 445 ; and 



'6 ' Descent of Man,' 2nd edit., p. July, p. 159. Also in 1867, 'On the 



32. influence of Age in Hereditai-y Diuease.' 



