SEA-URCHINS AND SEA-CUCUMBERS 841 



the first thing that strikes us is, that a framework or skel- 

 eton of extreme delicacy, composed of glassy rods, sup- 

 ports 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 direc- 

 tion, but a little diverging; and two other shorter rods 

 pass down from the front of the ring, parallel to these. 

 After a while each lateral pair of rods is united by a short 

 cross-piece, and the result is four lengthened rods, two 

 of which go down through the visor into the chin-points, 

 and two larger and stouter ones through the ears into the 

 shoulder- points. This, then, is the solid skeleton, the in- 

 terest of which is much enhanced, when we observe that 

 it is formed, on the common plan, out of perforated lime- 

 glass, the two ear-rods and the crest-rod being pierced with 

 a regular series of oval holes, and bearing on their edges 

 corresponding projecting points. 



Now, to turn again to the gelatinous flesh. The inner 

 surface of the visor, or that which would be in contact 

 with the face of the wearer, supposing it to be a real 

 helmet, has a great squarish orifice with a thickened mar- 

 gin, which we see by its movements to be highly sensitive 

 and contractile. This square orifice is the mouth of the 

 larva, and it leads into a cavity in the upper part of the 

 visor, which is the gullet; and this in its turn terminates 

 in a narrowed extremity, which passes into the orifice of 

 a greater and higher cavity, the lip of which embraces it 

 just as the bung- hole of a barrel receives and embraces 

 the tube of a funnel. The latter cavity occupies the chief 



