1310 THE STORY OF THE UNIVERSE 



From its appearance when brought up Holtenia 

 evidently lives buried in the mud to its upper fringe 

 of spicules. When freshly dredged, it is loaded with 

 pale gray semi-fluid sarcode, full of Globigerinae, 

 Triloculinae, and other rhizopods, and covered in our 

 northern localities with the little ophiurid Amphiura 

 abyssicola, Sars, and the exquisitely delicate trans- 

 parent clam, Pecten viterus Chemnitz. Holtenia 

 extends from the Butt of Lewis to Gibraltar, in 

 from 500 to 1,000 fathoms. 



In the Hexactinellidae all the spicules, so far as 

 we know, are formed on the hexradiate plan; that is 

 to say, there is a primary axis, which may be long 

 or short, and at one point four secondary rays cross 

 this central shaft at right angles. In many of the 

 Hexactinellidae the spicules are all distinct, and com- 

 bined, as in Holtenia, by a small quantity of nearly 

 transparent sarcode; but in others, as in "Venus's 

 flower-basket," and the nearly equally beautiful 

 genera Iphiteon, Aphrocallistes, and Farrea, the 

 spicules run together and make a continuous silicious 

 network. When this is the case the sponge may be 

 boiled in nitric acid, and all the organic matter and 

 other impurities thus removed, when the skeleton 

 comes out a lovely lacy structure of the clearest 

 glass. The six-rayed form of the spicules gives the 

 network which is the result of their fusion great 

 flexibility of design, with a characteristic tendency, 

 however, to square meshes. 



Off the Butt of Lewis, in water of 450 to 500 

 fathoms, we met on two occasions with full-grown 

 specimens of a species of the remarkable genus 



