140 . LIFE BY THE SEASHOEE. 



dwellers, with great rapidity, and the enthusiastic naturalist 

 is often wise to take with him a cautious and unenthusiastic 

 companion and a flat-bottomed boat. He will soon learn by 

 experience whether the element of safety imparted by the 

 presence of the boat compensates for the trouble of wading 

 for perhaps half a mile through water too shallow for it to 

 move or laboriously pushing it over the sandy flats. All 

 these are mere trifles to the genuine enthusiast, and if the 

 ground be rich, sand digging becomes a delightful and profit- 

 able amusement. You may get many curious creatures, but 

 there is at least this satisfaction in regard to the heart- 

 urchins, that if you find any at all you are pretty sure to 

 find as many as you can possibly want. They occur at no 

 great depth below the surface, in burrows of their own 

 making, and many are at times turned up in each spadeful 

 of sand. In life they are of a beautiful golden colour, 

 which unfortunately speedily fades after death, and the tests 

 are so fragile that they are often broken to pieces in the 

 mere handling and separating from the sand. 



As regards structure, notice first the silky spines, which 

 vary much in size, and are not uniformly distributed over 

 the surface. The test is somewhat heart-shaped, and flattened 

 beneath, and the mouth will be found on this lower flattened 

 surface, overhung by a lip-like process, but without any 

 trace of a lantern. Round the mouth, and sending two 

 diverging horns backwards, is a bare space, perforated, 

 especially near the mouth, by pores through which a few 

 tube-feet emerge. These are somewhat complicated in 

 structure, having curious brush-shaped tips, and function as 

 tentacles. Between the posterior diverging horns just men- 

 tioned is a group of interesting spines. They are stout and 

 flattened at the ends, or spatulate. It is these which are 

 used in excavating the burrow, their action being assisted 

 by the other spines, which have an interesting and somewhat 

 complicated arrangement, well worth careful study, and by 

 the mouth process. Next turn over your specimen and 

 study the dorsal surface. In a living specimen it is possible 

 to make out, though less clearly than in the dry shell, that 

 the ambulacral areas in this region show what is called a 

 petaloid arrangement, that is, they are arranged roughly 

 speaking in the form of a five-rayed star, and are thus 



