538 



SPONGES. 



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 

 Dictyonina. 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 Lyssacine sponge, which has diverged but slightly from the simple sac form, was 

 dredo-ed 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' flower-basket {Euplectella), shown in the central illustration of the 

 coloured 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 surrounded 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 10 to 18 inches in length, shaped like a cornucopia, 

 the curve taking place at the junction of the lower and middle third. Euplectella 

 oiveni from Japan, which closely resembles E. aspergillum, 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, characterised 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 anchor the sponge in the mud. For a varying distance below 

 the body, the tuft is invested by a parasitic zoophyte. A transverse section of 

 the cup shows a cavity, in the centre of which is a spike which is the upper 

 <nd of the glass-rope projecting into the interior. From the central spike septa 

 radiate ; these are convex along their upper margins, and attached at their 

 ends to the imperforate bands on the operculum. The walls contain the much- 

 folded layer of flagellated chambers. 



The spicules of the tuft are pointed at the upper end, and terminate below in 

 minute four-pronged anchors. Many of them are marked with a spiral ridge, 



