PORIFEHA. 



217 



Amongst the calcareous Sponges, the simple Sponge with inhalent 

 pores and terminal osculurn (Olynthus-fown) is represented by the 

 stock-forming Leucosolenia (Grantiu), which is composed of numerous 

 hollow cylinders. The structure of this sponge 

 has been described by Lieberkiihn. 



In the Syconidoe the body cavity has a more 

 complicated form. The central space opens into 

 secondary peripheral spaces or radial tubes, which 

 are lined by ciliated cells, and open externally 

 through the inhalent pores (fig. 162). 



In other calcareous Sponges (Leuconidcc] the 

 radial canals have the form of irregular parietal 

 canals, giving oft* branches to the periphery and 

 possessing dilated, ciliated chambers. This form 

 of internal canal system is also found in most 

 of the stock-forming, silicions Sponges (fig. 163). 



Sponge forms may become more complicated 

 by the formation of stocks ; the originally simple 

 Sponge, which has developed from a single cili- 

 ated larva, gives rise by budding and incomplete 

 fission to a polyzoid sponge body; or several 



originally 



separate 

 individu - 

 als, each 

 of which 

 has origi- 

 nated from a single larva, 

 fuse together to form a com- 

 pound sponge stock. Both 

 these methods of growth are 

 repeated in a similar manner 

 in the formation of the stocks 

 of Polyps (fig. 164). In the 

 same way that the fan-like 



FlG. 163. Section of Curticium candelabrum (after nets of the Fan C'ul'al (//////'/- 

 JFr. E. Schulze). <Jk, Ciliated chamber of tbr / / j ij \ i 



parietal canal. dogwgw. JlaMlum) are formed 



by the repeated fusion of its 



branches, the gastrovascular cavities of which anastomose, so also 

 in the case of the branching sponges, as a result of the same pro- 

 cess, reticulate, or coiled or even massive stocks are formed (fig. 165). 



FIG. 162. Longitudinal 

 section through Sycon 

 raphanuit, slightly mag- 

 nified. 0, Osculum 

 with collar of spicules ; 

 Et, radial tubes which 

 open into the central 

 cavity. 



