325 



Among the lower forms we find sea-hedgehogs, that is, "sea- 

 urchins," and "sea-cucumbers." It is of these I would now briefly 

 speak, as they are among the interesting things which the visitor to 

 the sea-side will be sure to find, if he search faithfully for them. But 

 first as to the sea-urchins (Figs. 26, 27). If one would study these 

 strange forms, he must seek for them in the deeper pools left by the 

 tide. Nor is a casual glance into the pool sufficient to reveal the prize 



Fig. 26.— Sea-Ubchin (Toxonneustes drobachien- 

 sis, Agassiz). 



Fig. 27.— Top- View of SEA-URrmrr, 

 Spines removed. Shows ambii- 

 lacral and iuterambulacral plates. 



"which he is in search of. The beginner may look into a clear pool 

 where there are a hundred sea-urchins, and perhaps he will not see 

 one until he has looked for some minutes ; for sea-urchins not only 

 resemble some of the sea-weeds in their color, but by means of their 

 locomotive suckers they draw the sea-weeds closely about them, in 

 many cases completely concealing themselves. If the collector reach 

 down into the water the full length of his arm, and move his hand over 

 the bottom among the sea-weeds, he will not be long in finding a sea- 

 urchin. He will know when he touches one, as the sharp spines stand 

 out on every side. Without moving from his position the collector will 

 often secure a score or more of fine living specimens — some hardly 

 exceeding a fraction of an inch in diameter, and others two inches or 

 more ; for he will find them of difi'erent ages, even if not of different 

 species. Should he put them in a shallow pool while he goes on col- 

 lecting, and then look for them again, he will at first think they have 

 escaped into the sea or into some hole ; for, true to their instincts, 

 no sooner are they uncovered than they begin to conceal themselves 

 again by drawing around them the sea-weeds by means of their long 

 locomotive suckers. If we turn one over on his "back," that is, 

 place the mouth upward, the urchin immediately begins to turn itself, 

 and in a short time will regain its natural attitude, mouth downward. 



The spines are very remarkable, not only in their appearance, but 

 in their structure. A cross-section of one, under a microscope, reveals 

 a structure so perfect and so beautiful that the richest mosaic is but 

 rude masonry as compared with this natural mosaic. 



Situated among the spines are curious three-pronged forceps, which 

 have much puzzled the naturalists in days gone by ; for it was doubtful 



