78 Introduction to Animal Morphology. 



are uniform, simple, with stellules. Steletta has both simple 

 and anchorate spicules. The central spicules in Geodia 

 are grouped in long, radiating fascicles. Placospongia is 

 branched like a coral, with a central axis separated from the 

 •cortex by a sarcode layer. 



Order 6. Acanthospongia — including the Hexactinellae of 

 Schmidt; siliceous Sponges with hooked, anchorate, triradiate, 

 or stellate spicules, separate or soldered into a continuous 

 network. The sarcode is soft, and contains little dif- 

 ferentiated matter. Euplectella,^the beautiful " Venus' flower 

 basket" of the Philippines, has the upper end of its tubular 

 cavity closed with a flinty network. Hyalonema has a long 

 twisted " glass rope" of spicules around the elongated 

 osculum (cloaca). Esperia has spindle-shaped or linear 

 needles, with hooks, anchors, &c., in the membrane or 

 sarcode ; the personce in some Esperiae are polypoid and 

 bilaminar. Dactylocalyx is massive, with the spicules anky- 

 losed into a coral-like, expanded mass. Aphrocallistes is 

 tubular, with a net-like, continuous skeleton of siliceous 

 threads. Holtenia is a remarkable bearded form, dredged in 

 the North Atlantic. Allied to this order is the group 

 Lithistidse, proposed by SchiJiidt for Sponges with a con- 

 tinuous skeleton, but without hex-radiate spicules. 



Order 7. Potamospongia — massive or branched, often 

 green,* freshwater Sponges, with siliceous spicules united by 

 Spongiolin threads ; the ova have a coriaceous, spiculigerous 

 envelope. This includes the Spongillae of our rivers 

 (S. fluviatilis) or lakes (S. lacustris), which have smooth or 

 echinulated (S. echinata) spicules. 



Order 8. Calcispongia — mostly littoral, smooth, white 

 Sponges, with calcareous, acicular, or triradiate spicules. 

 They may be single personae, with (Monosyca) or without a 

 mouth (Clistosyca) ; or colonies with one (Coenosyca) or 

 many mouths (Polysyca) ; or a stock may have no mouth 

 (Cophosyca). The body wall may be solid, or pierced by 

 simple pores, or by regular or irregular canals. Many of 

 them develop sexual products, the spermatozoa being the 



* Containing Chlorophyll. 



