1897] 357 



CORRESPONDENCE 



INHERITANCE OF ACQUIRED CHARACTERS 



In view of the doctrine which constitutes the corner - stone of Prof. Weismann's 

 theories of heredity — the non -inheritance of acquired characters — any exceptions to the 

 rule which he lays down may be worth notice. I desire to submit to your readers for 

 consideration one which has appeared to me to bear upon this question — viz., the direc- 

 tion in which the hairs slope on the extensor surface of the forearm in certain hairy 

 Quadrupeds and in man. The course which the hairs take on this small area varies in 

 ifferent animals, but, as far as I can learn, in two main directions only. In the first of 

 these, which one may look upon as more ' normal, ' the slope is on the whole directed 

 in the axis of the limb towards the distal extremity, and is thus in keeping with the 

 general slope of hair on the other areas of this and the posterior extremity of the animal, 

 as in the great Ungulate order and a few species of monkeys. The second type of direc- 

 tion presents a certain reversal of the slope — viz., that the hairs after a mauus-ward 

 course on the flexor surface curve round the lateral borders of the fore-arm, and when 

 they reach the extensor surface they pass in a reversed direction, in some animals on the 

 whole area, in others on the proximal portion only, towards the trunk. This second 

 type is seen clearly in man at all ages, in the anthropoid apes, especially in the long- 

 haired Orang, to an extent exceeding any other animal I have seen, in most lower 

 monkeys, and in the Carnivores. In the last-named order the direction is visible in the 

 terrestrial Carnivores, Arctoidea, Cynoidea and Aeluroidea, especially in the shorter- 

 haired forms, but in those with longer hair on the limbs the general set of hair on this 

 area is towards the trunk, even if indistinct in some. It is the second of these types to 

 which I would draw attention as being a departure from the first, which is seen in 

 Ungulates, and which is more in accordance with the natural arrangement of hair. In 

 this great group of animals, the Ungulates, there is a very general habit of flexing the 

 fore-limb in the attitude of repose, as one sees commonly in a herd of cows and horses 

 grazing, when these limbs lie doubled up and the hoofs are resting under the fore part 

 of the trunk. The same position can be observed in other families of this order in con- 

 finement. A similar slope of hair is also seen in certain Marsupials, Kangaroos, for 

 example ; and in these animals, which almost always lie on their sides when at rest, the 

 position would be indifferent as to influence upon the slope. In Ungulates the pressure 

 thus exercised when the limb is in acute flexion would act at right angles to the axis of 

 the limb, and, except in so far as it would confirm the original slope of the hair on the 

 extensor surface, it would be indifferent in its effect on the hair-slope. But in the 

 Primates, Carnivores, and certain other animals in which the surface of this limb-seg- 

 ment in question is exposed to pressure acting in a different manner, one is not surprised 

 to find a different slope of hair. In Man it is frequently subject to pressure against some 

 underlying fixed surface. In apes and monkeys of all kinds it is extremely common in 

 their sitting posture to see their upper extremities strongly flexed at the elbow and rest- 

 ing against their lower limbs. In terrestrial Carnivores the normal attitude of repose 

 is, except on the occasions when they lie • asleep stretched out on their sides, that the 

 fore-limbs are planted in front of the trunk, seen most noticeably in the ' couchant ' 

 position which they commonly assume. In all these instances it is obvious that there is 

 a slowly acting mechanical force in the downward and forward direction by reason of the 

 weight of the limb itself, and the fore part of the trunk which is supported by it. The 

 effect of this pressure would be to cause the hairs to slope towards the trunk, as is found 

 to be the case in these animals. There are of course many apes and monkeys, notably 

 the chimpanzee, gorilla, and orang, in which the same direction is taken by the hairs on 

 other aspects of the same limb on regions where no pressure can influence it. In these 

 the general set of hair towards the trunk is probably due in part to the effect of gravi- 

 tation on the long hair, and perhaps, as Mr Wallace has suggested, to the influence of 

 heavy rain in tropical forests when the hair would act to the body as thatch does to the 

 roof of a house. 



The direction of hair-slope on this area is, of course, congenital ; it is therefore a 

 primary character, not one acquired by the individual through secondary forces. It is 

 congenital in the human infant, in the young monkeys and young Carnivores which I 

 have been able to examine, and presumably it is so in all in which it is found. 



