LEAF-ROLLING CATERPILLARS. 363 



size of the caterpillars, had noticed that the muscular strength 

 of the insect was quite inadequate to the work which was done. 

 That much of it was owing to the " bowsing " system, which 

 has already been described when treating of the Toggle-joint, 

 was very probable, but that some other force must be employed 

 was evident. 



On unrolling a leaf, the hidden force was at once explained, 

 and showed itself to be a system of accumulators exactly like 

 those of the pistolograph or the catapult. The caterpillar spins 

 successive belts of silken threads, and affixes them to the leaf, 

 as shown in the illustration. These threads are nearly as 

 elastic as the india-rubber bands of the catapult, and accord- 

 ingly draw the leaf together. Another set of belts is added 

 above the former, and, as they harden and contract in the 

 air, they roll the leaf still further. The first row is then 

 shortened and tightened, and a third and fourth row are 

 added in the same fashion. So elastic are these belts, that if 

 the leaf be carefully handled it can be almost wholly unrolled, 

 and will spring back again as soon as the force is removed. 



ANOTHER form of accumulated force may be seen in the 

 ordinary Carriage Spring, one of which is shown in the illus- 

 tration. It is made of a number of strips of elastic steel lying 

 upon each other, and suffered to play upon each other by 

 means of slots and rivets. The weight being placed in the 

 centre, it is evident that this very ingenious spring is really an 

 elastic girder, yielding to sudden pressure, and recovering 

 itself when that pressure is removed. 



INGENIOUS as is this spring, it has many parallels in Nature, 

 one of which is here given. 



It is popularly thought the hoof of the horse is a solid mass 

 of horn destined to protect the feet against hard and rough 

 ground. Such certainly seems to be the opinion of farriers, 

 who, in shoeing horses, act exactly as if the horn of the hoof 

 were structureless ; whereas it is a marvel of complicated 

 mechanism. On looking at the exterior of a horse's hoof, it 

 will be seen to be marked with a vast number of very fine, 

 but easily visible longitudinal lines, looking as if they were 

 scratches from a very fine needle. If the hoof be removed 



