CLASS SPONGIA. 



tains. We can think of the sponge, then, as a colony* 

 of protozoan animals, each living a separate life, though 

 interested in the welfare of its neighbors. The water, 

 after having been examined by these flagellate cells, 

 passes on into a central cavity, and finally leaves the 

 sponge through a large opening at the apex. 



Often attached to the side of this more simple 

 sponge are so-called "buds," which are young sponges in 

 process of growth. 



ORDER HYALOSPONGIA (hi al o spun'ji a). 



Silicious, or Glass Sponges, are less common.f 



ORDER CERAOSPONGIA (se ra o spun'ji a). 



Sponges having a horny skeleton are those with which 

 we are most familiar. If a common bath* sponge, Euspongia 

 adriatica (u spun'ji a ad ri at/I ka), be examined, there will 

 be found small pores, leading in at the sides, while at the 

 apex are the large excurrent openings. Those who cure 

 the sponge, wash away the soft flagellate cells together 

 with other slimy portions of the animal's body. All the 

 more valuable forms are found in the warmer regions. 



We have thus seen that the Porifera are animals whose 

 bodies consist of numerous cells, supported by a frame- 

 work, or skeleton. Until recently, the members of this 

 Branch were considered by many naturalists as plants ; 

 but the working out of their life-history has proved them 

 entitled to higher rank than some other animals. 



* "It is a kind of sub-aqueous city, where the people are arranged about the 

 streets and roads in such a way that each can choose his food from the water as 

 it passes along." HUXLEY. 



t The most beautiful is the Euplectella aspergillum (fl plgk'tel la 5s per gil'lumt, in 

 which the silicious fibers form a delicate mesh of lace, known as Venus' Flower 

 Basket, formerly considered a unique specimen of Chinese industry. 



