PORIFERA. 



Phylum II. PORIFERA (Sponges). 



Multicellular animals, chiefly marine ; body penetrated by a 

 complex series of canals, into which the water enters by the 

 pores of the wall. These canals widen out into, or give off at 



intervals digestive chambers, and fin- 

 ally converge into one or more large 

 canals which open on the upper side 

 of the sponge in large craters or os- 

 cula. (Fig. 21.) Most modern sponges 

 secrete a skeleton of horny fibers, 

 which is frequently reenforced by sili- 

 cious spicules of various forms. In 

 many extinct types these spicules were 

 the most prominent structure, and fre- 

 quently became thickened and united 

 to form a solid trellis or framework 

 Fig. 2i. Diagrammatic figure which retained the form of the sponge 

 showing the structure of a simple on fossilization. In some sponges this 



framework is regularly reticulated, in 

 others it consists of very irregular 

 branching spicules, while in still 

 others it is apparently a solid mass 

 of spicules. Some forms {Dictyospon- 

 gia, etc.) were apparently delicate nets 

 of siliceous fibers, the form and im- 

 pression of these being preserved by 

 the infiltrated sand as an internal 

 mold. 



Sponges as a rule are poorly pre- 

 served and difficult of determination. 

 They have been but little studied in this country. 



sponge in vertical section. The 

 sponge substance {fl ) is lightly 

 shaded. The canal system is black, 

 the arrows showing the direction 

 of the currents, fp, are the pores 

 or openings of the inhalant canals 

 (epirrhysa) which lead to the 

 flagellate chambers, ch. From the 

 latter depart the exhalant canals 

 (aporrhysa), ic, which open into 

 the general cavity or paragaster. o, 

 is the osculum or aperture through 

 which the water is discharged. 

 ^Haeckel, in Hall and Clarke.) 



Literature. 

 i860. Roemer Ferd. Silurische Fauna des Westlichen Tennessee. 

 1889. Beecher, C. E. Brachiospongidae, Mem. Peabody Mus. Yale 

 Univ., II, pt. I. 



1898. Hall, J., and Clarke, J. M. Palaeozoic reticulate sponges. 

 Mem. [I. N. Y. State Museum. Also papers by Whitfield Hall and 

 others. 



