CHAP. VIL] THE DEEP-SEA FAUNA. 427 



or slightly-cupped disk, with a papilla in the centre 

 receiving the upper end of the coil, with large oscular 

 openings, and a fringe of delicate radiating spicules 

 round the edge, was the top of the sponge, spreading 

 out prohably level with the surface of the ooze. 



In essential structure Hyalonema very closely re- 

 sembles Holtenia, and the more characteristic forms 

 of the Hexactinellidae. The surface of the sponge is 

 supported by a square network, formed by the sym- 

 metrical arrangement of the four secondary rays of 

 five-rayed spicules, and the sarcode which binds these 

 branches together is full of minute feathered five- 

 rayed spicules, which project from the branches like 

 a delicate fringe. The oscula are chiefly on the upper 

 disk, and lead into a number of irregular passages 

 which traverse the body of the sponge in all direc- 

 tions. When we trace its development, the coil 

 loses its mystery. On one of the Holtenice from the 

 Butt of the Lews, 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 species, 

 each showing unmistakeably the characteristic forms 

 of its special spicules. Most of them were the young 

 of Tisiphonia y but among them were several Holteniw, 

 and one or two were at once referred to Hyalonema. 

 In two or three hauls in the same locality we got 

 them in every subsequent stage beautiful little 



