THE SPADE. 225 



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 throw- 

 ing 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 con- 

 cealing 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 regu- 

 larity must be observed, in order to allow space to be accu- 

 rately 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. 



The reader will remember that in the preceding description 

 of the Heart-urchin it was mentioned that many of the 

 spines are shaped at their ends something like spoons, and 

 that their comparatively wide blades are used in scraping the 

 sand and shovelling it aside. In fact, these flattened spines 

 are natural spades, used on the same principle as the modern 

 spade of civilisation. 



On the right hand of the illustration are shown two forms of 



