SIX-RAYED OR GLASS-SPONGES 3513 



soft- walled sac of this description, one axis being vertical to the walls, and the other 

 two tangential; the rays of each spicule uniting with those of adjoining spicules to 

 form a framework. The typical spicule has six equal rays at right angles to each 

 other, with an axial canal in the centre of each. When four of the six rays dis- 

 appear, leaving only a glassy rod, the history of such a spicule is betrayed by the 

 presence of a minute cross, which is all that remains of the axial canals of the 

 atrophied rays. Endless modifications of the typical form may occur. One or more 

 of the six rays may develop more than the rest; one or more may be suppressed, 

 resulting in the formation of five-, four-, three-, two-, or one-rayed spicules. 

 Again, the simple principal rays may branch or give off tufts, which may be 

 pointed or end in discs. Further, the rays may be curved, or become beset with 

 spines. The spicules either remain loose and separate in the soft tissues or become 

 joined by apposition and intertwining, or by fusion of rays by means of layers or 

 bars of siliceous cement. 



The glass-sponges are divided into two groups, the Lyssacina and the Dictyo- 

 nina. In the former the spicules are loose and separate, fusion when present 

 occurring in the older parts of the sponge; in the latter the principal spicules form a 

 solid framework even in the earliest stages of growth. Bathydorus, a I^yssacine 

 sponge, which has diverged but slightly from the simple sac form, was dredged 

 from two thousand nine hundred fathoms in the North Pacific, and forms a soft 

 thin-walled tube about seven inches in height and two inches in diameter. In the 

 Venus' s flower basket {Euplectella} , shown in the central illustration of the colored 

 plate, there are certain modifications of the simple sac type. Firstly, there is a lid 

 at the top, and further, the walls of the tube are perforated by large round holes 

 about one-twenty-fifth of an inch in diameter. The water can thereby pass direct 

 from the outside into the gastral cavity or lumen of the tube, each aperture is sur- 

 rounded by an iris-like membrane which can probably close the orifice. These 

 parietal apertures, in the whole thickness of the wall, must not be confused with 

 the very minute in-current pores through which the water passes into the sponge 

 substance. In life, the glassy framework frequently seen as an ornament is 

 covered with the brownish gelatinous flesh. The glassy skeleton forms a curved 

 tube from ten to eighteen inches in length, shaped like a cornucopia, the curve tak- 

 ing place at the junction of the lower and middle third. Euplectella oweni from 

 Japan, which closely resembles E. apsergillum, forms a straight cylinder, devoid of 

 the collar round the lid and without ridges on the walls. 



The glass-rope sponge (Hyalonema) of Japan belongs to a group of Lyssacine 

 sponges, characterized by the possession of amphidiscs, spicules with a straight 

 shaft, at each end of which is a large toothed disc, resembling the ribs of an 

 umbrella. The spicules are sometimes large enough to be visible to the naked eye, 

 and vary in different species from the hundredth to the twenty-fifth of an inch in 

 length. The rope was first brought to Europe about 1830, and for years formed 

 the subject of controversy as to its nature. The Japanese glass-rope sponge forms 

 a solid-looking, ovoid, thick-walled cup, the top of which is closed by a thin sieve- 

 like lid with an imperforate cross-shaped area. From the lower end of the body 

 arises the long siliceous glass-rope, composed of twisted strands of spicules which. 



