148 



KNOWLEDGE. 



[July, 1902. 



on the l>ai'k. The lower half aud most of ilio forearm are 

 iMjually Simian anil Himple. The only except ion on the 

 forearm is the reversed slope on the extensor surface, due, 

 I siibmit, to the resultant of two foroes. a downward and 

 forward one,actin>,' when tliis part of the linih rests on 

 any object, as it frequently does. Tliis jioint does not 

 distinguish man ranch from ajies and monkeys, and in all 

 of these grouj^s similar mechanical forces operate to 

 produce it, including in the latter the effect of tropical 

 rain, in their arboreal lives. I have referred at much 

 more length to the causation of this hair-slope else- 

 where,* and need only say here that it is more 

 ]in)lial)le that adaptation hij habits aud use is a far more 

 intelligible cause for it than any adaptation to the needs 

 of the animal on which selection might act. This pecu- 

 liarity is found very marked in carnivores, such as a short- 

 haired doi;, and ungulates such as certain antelopes, which 

 lie with their fore limbs planted in front of them, in the 

 very attitude calculated to produce this slope. 



On the lower extremity the direction of hairs is as simple 

 and primitive as that on the nj)per is complicated and 

 acquired. The only area worth noting is the upper third 

 of the back of the thigh, where the effect of the sitting 

 attitude is clearly able to produce the direction indicated. 

 On the rest of tLis limb so few forces act on the skin 

 surface with any uniformity that it has retained its 

 primitive slope of hair. 



It is worth noting that the theory of use-inheritance 

 carries with it the view that the effects of disuse are 

 inherited, and this is remarkalily illustrated by the way in 

 which in a very hairy subject, the growth of hair on the 

 leg ceases sharply at a point opposite to the ankle-joint. 

 It is difKcult to see how any other influence than that of 

 the friction of a shoe or low boot can produce this sudden 

 transition from a hairy leg to a nearly hairless foot. The 

 contrast also in a very hairy man between the great amount 

 of hair on the back of the hand and the appearance of 

 scattered long hairs on the instep of the same subject is 

 most suggestive. 



In addition to any interest possessed by these facts, 

 they have a bearing on heredity. The inference to be 

 drawn from them seems to be that acquired characters 

 may, and in this case are, inherited. If the descent of 

 man be what it is claimed to be, he has somehow acquired 

 and ti-ansmitted a very remarkable series of changes of 

 hair-direction. It would seem that these can only have 

 arisen through habit, use, and the action of environments, 

 and by disuse, and that any reference of them to selec- 

 tion is estopped. There is no hair- tract of the human 

 body diverging from the ancestral type of slope which has 

 not an adequate and ascei-tainable mechanical force to 

 which the facts may fairly be attributed. 



Tlip illustrative plate lias been prepared under my direction by 

 Mr. R. E. Holding, who has greatly assisted my demonstration of the 

 nihjpft. 



FORE-LEGS AND THEIR USES. 



By E. A. Butler, b.a., b.sc. 



The common lobster furnishes one of the best possible 

 illustrations of a curious principle that finds expression in 

 the organiiiation of animals whose body, like its own. is 

 composed of a succession of segments with jointed 

 appendages, or in other words, animals belonging to the 

 great sub-kingdom Arthropoda. The principle in question 



* Proe. Zoological Socicft/, London, June. 1903, pp. 676-77 ; 

 " Journal of .inatomy and Plivsiology," Vol. XXXV., p. 319 ; " Use- 

 Inheritance," pp. 2S^33. 



is that the paired appendages of the different segments, 

 though all construct<!d upon the same plan, may become 

 so modified in form as to be adapt<.'d to the discharge of 

 the most diverse functions. And so we find that in this 

 particular animal these appendages subserve the functions 

 of progression, whether by walking or swimming, of 

 attack and defence, of manipulation and mastication of 

 the food, and of sensation of various kinds. Amongst 

 insects, too, which are equally arthropodous animals, we 

 find that those apjMindages which have assumed the 

 character of limbs, and are, as a rule, adapted for locomo- 

 tion of some kind or other, may yet, by still further 

 modification of their form, become well suited for the 

 performance of other functions quite remote from their 

 original purpose. It is the first of the three jiairs of legs 

 with which an insect in its adult condition is furnished 

 that exhibit this peculiarity in the greatest degree, and I 

 propose in this paper to consider in detail the varied 

 functions which are discharged by these same limbs 

 amongst British insects. 



We may distinguish in these fore-legs six different 

 types, which are generally distinct, not merely in function, 

 but also in shape and appearance. They may be called 

 the ordinary locomotive type, the prehensile, the raptorial, 

 the fossorial, the auditory, and the brush type ; or, to jmt 

 it in other words, insects may use their fore-legs to aid 

 them in walking or running, in clasping and retaining their 

 mates, in catching their prey or in steadying it while it is 

 being devoured, in digging through the soil, and even in 

 listening to insect music, or again, their front legs may be 

 shortened and covered with a dense mass of hairs so as to 

 look like a brush, and to be quite useless for walking. 



By far the greater number of insects of eom-se use their 

 fore-legs as they do the other pairs, for locomotive 

 purposes, and we may consider the locomotive as the 

 normal type of leg, and the rest as modifications of this. 

 As we shall have to make frequent reference to the 

 different parts of the leg, it is verv desirable that the few 

 technical terms it will be necessary to use should be 

 thoroughly grasped once for all, in order that the rest of 

 the paper may be intelligently followed. What then is 

 the construction of the ordinary locomotive legr It is 

 composed of five parts (Fig. 1). Beginning where the 

 leg joins the body, we 

 find first, the coxa, a joint 

 which varies very much 

 in shape, but always 

 attaches the leg to the 

 general armature or ex- 

 ternal skeleton, in a cavity 

 into which it exactly fits. 

 The shajie of the coxa 

 and the method of its 

 attachment determine the 

 directions in which the 

 leg as a whole can move, 

 and fix the limits of its 



action. A small joint comes next, called the trocJiaiiter. 

 This is succeeded by the two main divisions of the leg, 

 viz., the thigh ov femur, and the tibia or shank. Finally 

 we have a set of two, three, four, or five sm.all joints, 

 called collectively the tarsus, or foot, and at the end of 

 the last joint there is usually a pair of hooked claws. The 

 tarsus is the only part of the leg that comes in contact 

 with the ground, and its many jointed condition gives it 

 the necessary flexibility for securing firm foothold when 

 the insect is travelling over uneven surfaces, as would 

 nsu.ally be the case. At the points of junction of the 

 different divisions of the leg, the Ijend is successively in 

 opposite directions, just as in our own limbs. Thus the 



Fig. 1.— Le;,' of Stag Beetle. 

 c, coxa; f, trochanter; /, femur; 

 s, tibia ; d, tarsus. 



