SPONGE-CRYSTALS. 235 



give a greater treat to an intelligent but unscientific 

 friend then by placing an atom of woolly stuff, scraped 

 from the surface of a rock with a pin's point, beneath 

 a good microscope with a rather high power on, and 

 bidding him peep. I am sure you would have been 

 charmed with the sight I have had this morning ; 

 I was both surprised and delighted myself. 



Going carefully over, w^ith a triple lens, a frond of 

 NitopJiyllum laceratum, that I obtained a day or two 

 since at Hele, — the same frond, by the way, that had 

 already yielded me the interesting Tuhnlijiora jiahel- 

 lariSy — my eye was caught by what appeared to be the 

 ends of the tubes of some larger species of the same 

 genus projecting from over the edge of the sinuous 

 and lacerated frond. I immediately transferred it to 

 a glass cell, and applied it to the stage of the com- 

 pound microscope with a power of 220 diameters. 

 To my astonishment a mass of starry crystals met 

 my view, entangled among each other almost as thick 

 as they could lie, bv scores, nav bv hundreds. For 

 a moment the eye was bewildered by the multitude of 

 slender needle-like points crossing and reerossing in 

 every possible direction ; but soon the curious spec- 

 tacle began to take some kind of order ; the crystals 

 were seen to be all of one form, though varying con- 

 siderably in length and thickness ; they are three-rayed 

 stars, diverging at an angle of 120 degrees : the rays, 

 straight, slender needles, perfectly cylindrical except 

 that they taper to a fine point, smooth and transparent 

 as if made of glass, and highly refractive. 



These spiculee appear to me to be held together only 

 by their mutual entanglement and interlacing; their 



