PORIFERA [sponges]. 29 



with a serrated spiral ridge with the teeth pointing upwards High Case 



(Fig- 8). Table Case 



The body of the sponge forms a thick-walled cup, which, how- 2 a, b. 

 ever, is so loosely constructed that light can be seen through it. The 

 interior is divided up by four to eight vertical partitions radiating 

 from a central spike. The top of the cup is closed by a thin sieve- 

 plate with perforated " quarters " corresponding to the divisions 

 inside. A " commensal " zoophyte (PaJi/thoa) is always found 

 investing the upper end of the glass rope, and occasionally forms 

 pits (often mistaken for oscules) on the surface of the sponge itself. 

 Unfortunately the Palythoa has become detached from the upper 

 part of the root-tuft of the specimen figured, but is abundant on the 

 surface of the sponge body. The Japanese deep-sea shark-fishers 

 obtain the sponge by means of hooks attached to their deep-sea lines. 

 By a curious parallel, the deep-sea shark-fishers of Portugal obtain a 

 nearly allied species of Hyalonema in somewhat the same manner. 



Lophocalyx philippinensis, from Cebu (in fluid. Table Case 2a), 

 which forms a small compact thick-walled cup with long root-tufts, 

 furnishes a beautiful example of bud formation, buds of all ages 

 being present on the specimens. 



Sub-Order II. Dictyonina. In this group the skeleton, even in 

 the earliest stages, forms a rigid framework constructed of the fused 

 rays of large regular six-rayed spicules. These sponges usually have 

 a vitreous, finely honeycombed appearance. The magnificent 

 Aphrocallistes vastus (Fig. 1), in the centre of Case III., is shaped 

 like a vase with a thick stem, and with large folds projecting out 

 from the walls. The very fine specimen of Ghonelasma calyx, to the 

 right of the former, is bowl-shaped, and with finger-like pockets 

 often extending down, like the " roots " of a Banyan tree, till they 

 reach the base on which the sponge is growing. The fossil Ventri- 

 culites common in flints from the Chalk are Dictyonine Sponges. 



CLASS III.— DEMOSPONGI^ OR COMMON SPONGES. 



The Common Sponges include all sponges other than the 

 Calcareous and Glass Sponges. 



Tetractinellida (Four-Eay Sponoes). 



The sponges of this Order are often spherical with a radiating ^j^^^^^^^ ^^ ' 

 structure {Craniella, IV. 8), or they may form tough leathery cakes Partition. 



