SEA-URCHINS AND SEA-CUCUMBERS. 301 



with microscopic life ; and though many of your captives 

 will not long survive the loss of their freedom, still mean- 

 while you may secure many an interesting object, and 

 examine it while yet the beauty and freshness of life re- 

 main. And, moreover, with care and prudence, some 

 selected subjects may be maintained in vigour, at least 

 long enough to afford you valuable information on the 

 habits, economy, metamorphosis, and development of ani- 

 mals, of which even the scientific world knows as yet next 

 to nothing. 



I have just been so fortunate as to obtain in this way 

 one of our Sea-Urchins in its larva state, and have it now 

 in the thin glass trough which is on the stage of the micro- 

 scope. It is just visible to the unassisted sight as a slowly 

 moving point in the clear water, when the vessel is held up 

 to the light ; but with the low power which I am now 

 using, it is distinctly made out in all its parts, and is an 

 object of singular elegance and beauty. 



It is, as you see, somewhat of the figure of a helmet, 

 the crest rising to a perpendicular point, which is rounded, 

 the vizor or mask descending far down, and ending in two 

 points, and a long ear hanging down on each side, so as to 

 reach the shoulders of the wearer. Of course such com- 

 parisons are fanciful, but they assist one in intelligible 

 description. 



Now, the entire helmet is composed of a gelatinous 

 flesh of the most perfect transparency, so that we can see 

 with absolute clearness everything that is within it. And the 

 first thing that strikes us is, that a frame- work or skeleton 

 of extreme delicacy, composed of glassy rods, supports the 

 whole structure. Look carefully at this, and mark its 

 symmetry and elegance. There is, then, first, a rod which 

 passes through the crest perpendicularly, and carries at 

 its lower extremity a horizontal ring. To the opposite 

 sides of this ring are soldered two other very slender rods, 

 passing down nearly in a perpendicular direction, but a 



