342 EVENINGS AT THE MICROSCOPE 



part of the volume of the helmet, the four rods diverging 

 to enclose it. It is the stomach. 



It adds to the beauty of the little helmet- shaped creat- 

 ure, that while the greater portion of the substance is of 

 the most colorless transparency, the summit of the crest 

 and the tips of the shoulder-points are tinged with a lovely 

 rose- red. The whole exterior surface is, moreover, stud- 

 ded with those minute and glandular specks with which 

 every part of the adult Urchin is covered; and the light 

 is reflected from the various prominences with sparkling 

 brilliancy. 



The little creature moves through the water with much 

 grace, and with a dignified deliberation; the crest being 

 always uppermost, and the perpendicular position invari- 

 ably maintained. It does not appear capable of resting, 

 its movements depending on incessantly vibrating cilia. 

 These organs we perceive densely clothing the long ear- 

 pieces, but more especially accumulated and more vigorous 

 in a thickened, fleshy band, which passes partly round the 

 whole helmet, at the origin of these pieces. 



You do not discern the slightest resemblance of form 

 between this little slowly-swimming dome and the spined 

 and boxed Urchin which crawls over the rocks; and you 

 wonder by what steps the tiny atom of one- fortieth of an 

 inch in length is led to its adult stage. Fortunately I can 

 satisfy your curiosity on this point, not indeed from my 

 own observations, but by those of Professor Johann 

 Miiller, whose discoveries of the developments of these 

 and kindred animals are among the most interesting, be- 

 cause the most startling, of the marvels which modern zo- 

 ology has revealed to us. The whole process is full of 

 surprising details, to which the change of the caterpillar 



