1312 THE STORY OF THE UNIVERSE 



In essential structure Hyalonema very closely re- 

 sembles Holtenia, and the more characteristic forms 

 of the Hexactinellidae. On one of the Holteniae from 

 the Butt of Lewis, there was a little accumulation 

 of greenish granular matter among the fibres. On 

 placing this under the microscope it turned out to 

 be a number of very young sponges, scarcely out of 

 their germ state. They were all at first sight very 

 much alike, minute pear-shaped bodies, with a long 

 delicate pencil of silky spicules taking the place of 

 the pear-stalk. On closer examination, however, 

 these little germs proved to belong to different spe- 

 cies, each showing unmistakably the characteristic 

 forms of its special spicules. Most of them were the 

 young of Tisiphonia, but among them were several 

 Holteniae, and one or two were at once referred to 

 Hyalonema. In two or three hauls in the same local- 

 ity we got them in every subsequent stage beautiful 

 little pear-shaped things, a cehtimetre long, with a 

 single osculum at the top, and the wisp like a small 

 brush. At this stage the Palythoa is usually absent, 

 but when the body of the sponge has attained 15 mm. 

 or so in length very generally a little pink tubercle 

 may be detected at the point of junction between 

 the sponge body and the coil, the germ of the first 

 polype. 



During Mr. Gwyn Jeffreys's cruise in 1870, two 

 specimens of a wonderful sponge belonging also to 

 the Hexactinellidae were dredged in 374 fathoms in 

 rocky ground off Cape St. Vincent. The larger of 

 these forms a complete vase of a very elegant form, 

 nearly ninety centimetres in diameter at the top and 



