“Truly, these hairs are the feet with which he moves. The animal inhabits the sand at the bottom of the sea in our shallow bays, and burrows in it. By going carefully, with the lens at your eye, over the shell, you perceive that the spines, though all formed on a common model, differ considerably in the detail of their form. I have shown you what may be considered the average shape, but in some, especially the finer ones that clothe the sides, the club is slender and pointed; in others, as in those behind the mouth, which are the largest and coarsest of all, the club is dilated into a long, flat spoon; while in the long, much-bowed spines, which densely crowd upon the back, the form is almost uniformly taper throughout, and pointed.” “The animal sinks into the sand mouth downwards. The hard spoons behind the mouth come first into requisition, scooping away the sand, each acting individually, and throwing it outwards. Observe how beautifully they are arranged for this purpose, diverging from the median line, with the curve backwards and outwards. “Similar is the arrangement of the slender side spines; their curve is still more backwards, the tips arching uniformly outwards. They take, indeed, exactly the curve which the fore-paws of a mole possess,--only in a retrograde direction, since the Urchin sinks backwards,--which has been shown to be so effective for the excavation of the soil, and the throwing of it outwards. “Finally, the long spines on the back are suited to reach the sand on each side, when the creature has descended to its depth, and by their motion work it in again, covering and concealing the industrious and effective miner.” The reader will notice that this mode of digging is exactly like that which is followed by the users of the Digging-stick, the earth being first broken up, and the loosened portions thrown aside. The whole of the description of the spines is exceedingly interesting, but, as it does not bear directly on the present subject, I cannot admit it into these pages. * * * * * NOW comes another development in digging tools. We have already seen how effective an instrument a mere piece of stick can be in the hands of a skilful workman, and the manner in which it can tear up a given depth of soil. But, for agricultural purposes, something more is needed, and the ground must not only be broken up, but a certain regularity must be observed, in order to allow space to be accurately measured, and the crop apportioned to the area. Out of the Digging-stick, then, the Spade was developed, its chief advantage being that it dispensed with the use of the bare hands, and not only tore up the ground, but threw out the loosened soil.