SUBKINGDOM 



PORIFERATA (SPONGIJE). 



The Sponges are many-celled animals without a true digestive 

 cavity. They consist of protoplasmic matter in three cell-layers, 

 supported in most cases by a framework of horny (keratode) 

 fibres, or calcareous or siliceous spicules. The body-mass is 

 traversed by ciliated passages, which are dilated at intervals to 

 form chambers, lined with flagellated monad-like cells. Food is 

 obtained by currents of water, which is drawn in at multitudes of 

 inhalent orifices (pores), and expelled through a single or several 

 large openings (oscula). There are no further digestive or cir- 

 culatory systems, and no definite nervous organs. 



Reproduction takes place in the sponges by gemmation, and 

 also by fertilized ova. They are hermaphroditic. 



Sponges are divided into Calcispongise and Carneospongiae. 

 In the former the skeleton is calcareous spicules, disposed in lines 

 or columns at right angles to the walls, and the permeating ciliated 

 canals are w-ithout sacs. The latter class have a thick mesoderm, 

 cilia restricted to the chambers, and either no skeleton or a horny 

 or siliceous framework. 



The Calcispongiae are mostly extinct, and include the Palaeo- 

 zoic forms, Receptaculites and Stromatojyora. 



Carneospongiae include the only knoMni fresh-water genera, 

 Spongilla and Siphydora^ the common sponges of commerce 

 {Spongia), the boring Cliona, and the " glass-sponges," of 

 which the most beautiful is the Yenns' flower-basket {Euplec- 

 tella). 



Several hundred species of fossil sponges are described, rang- 

 ing from the Cambrian. 



No. 493. Astraeospongia meniscus, Roem. 

 Meniscus Limestoue (Niagara Group), West Tennessee. 



No. 494. Chenendopora fungiformis, Lamour. 

 Lower Greensand, Faringdon, Berks, England. 



