Carefully lay open several burrows and notice: (a) Whether the mouths of the burrows are plugged in any way, and, if leaves are used for this purpose, whether the leaves have been dragged into the hole (i) by the broad ends, (ii) by the narrow ends, or (iii) by the sides; do you find any signs of intelligence in the method adopted? (b) The length and width of the burrow and the character of its lining. (c) The end of the burrow; is it enlarged? Examine worm castings. Mark out a square yard of surface and collect, dry, and weigh all the castings found on this area in a certain time, say a month. Such observations should be made at different periods of the year, and over different kinds of soil, and comparisons made. Estimate the weight brought up per acre by worms during a year. Are the particles composing the castings very fine, fine, or coarse? Place worms in glass-covered flower-pots with earth of different degrees of firmness, and observe the methods of burrowing in loose and in firmly compacted earth respectively. Place pieces of leaf of carrot, onion, and cabbage on the surface, and at night observe how the worms grasp the pieces and drag them into the burrows. Earthworms.—Few people except naturalists have any idea of the vast number of earthworms living in the surface soil of this and most other countries, or of the importance of the work which they do. The common earthworm (Fig. 236) is much simpler in structure than any of the animals previously considered in this book. It is roughly [Pg 385] cylindrical in shape, though somewhat flattened on the ventral surface. It is divided into about 150 segments, which are marked on the exterior by grooves running round the body. The mouth is an opening in the first segment (Fig. 236, 1) and is overhung by a short fleshy lobe. The worm crawls along by alternate elongation and shortening of its body, being aided by short bristles which are directed backwards and act as pivots; limbs are entirely absent. The animal is very sensitive to touch, even to the vibrations of the ground; but it is stone-deaf, only just capable of distinguishing between light and darkness, and has very little sense of smell. Fig. 236.—Earthworm, seen from right side. 1, 15, 33, first, fifteenth, and thirty-third segments. (× ½.)