with particular regard to the Danish Fauna. 183 



also Solipeda. With the exceptions just mentioned, all Insects 

 are Plantigrada. 



It follows that Insects and Arachnida alone can svant foot-pads. 

 But whilst in Vertebrata the structure of the foot-pads is princi- 

 pally regulated by the weight of the body, the case is different 

 with the Arthropod a, because of their smaller size, firm external 

 skeleton, and enormous muscular power, together with the in- 

 creased number and different position of their limbs. Here the 

 object of the foot-pads is solely to assist the animal in standing 

 firmly on the ground, and to prevent the foot from slipping in 

 walking. Only those Plantigrade Insects, therefore, have foot- 

 pads whose mode of life requires that they should move on 

 highly inclined dry surfaces; and accordingly the foot-pads 

 consist of innumerable thick hairs, broader, softer, and more or 

 less divided towards their tips, collectively forming an even and 

 almost smooth surface under the foot, soft as velvet, which slopes 

 outwards towards the point of the foot. 



Two sets of neighbouring organs, spurs and claws, facilitate 

 the working of the foot-pads. 



The development of spurs depends on whether the legs are 

 constructed for walking or for running. In the first case the 

 limbs are shorter, all three pairs of equal length, and the joints 

 are during the movement inflected against one another in such 

 a manner that femur and tibia form together nearly a right 

 angle, as well as the tibia and tarsus. The position of the tibiae 

 is therefore perpendicular; and as the movement at the same 

 time is slow, the foot-pads afford sufficient security against 

 slipping, and the spurs are not at all developed, or, at any rate, 

 they remain very small, almost imperceptible. But if the limbs 

 are calculated for running, they are all proportionally longer, 

 the posterior pairs increasing in length; and the joints are, 

 during the movement, so inflected as to form more or less obtuse 

 angles. The longer the legs are, and the greater the difference 

 in length between the different pairs of legs, the more obtuse do 

 the angles become. The position of the tibiae is consequently 

 sloping outwards; and, the movement being at the same time fast, 

 the foot-pads do not afford sufficient security against slipping; 

 the spurs are therefore developed in proportion as their assistance 

 is needed. 



The claws play quite a different part. Indispensable as they 

 are for climbing on perpendicular surfaces, and for security 

 against sudden shocks, the claws would essentially impede walk- 

 ing, and render running almost impossible, on account of their 

 downward direction, curved shape, and sharp points, if there 

 had not been added some contrivance in order to suspend their 

 action whenever their service is not required, and to bring them 



