CHAPTER II 



POEIFERA 



THE next division of the animal kingdom in the ascending 

 scale is represented by the sponges. Here complexity com- 

 mences, but " tissues," as regards muscle, etc., are not yet 

 apparent, although foreshadowed. Some naturalists do 

 not admit the sponges as a group or Phylum by themselves, 

 but include them in the next viz. in the Ccelenterata 

 but the majority seem to be in favour of keeping them 

 separate 



The text-books thus define the Porifera : Animals with 

 soft bodies composed of a large number of cells, which cells 

 have the power of amoeboid movement. 



The structure is supported and maintained in form 

 either by a skeleton of horny fibres, by spicules of carbonate 

 of lime, or by spicules of silica. 



The mass is pierced by a vast number of pores (hence 

 Porifera, " pore-bearing ") opening into a series of canals, 

 which communicate with little hollow chambers digestive 

 cavities and each sponge has one or many " exhalent 

 apertures " (osculce). 



In adult life they are affixed and plantlike. In early 

 life they are active, and free swimming. They have different 

 methods of reproduction viz. : 



One by budding, by which means the mass extends 

 laterally and in thickness, for except in a few species there 

 is little precise form or size limit. They also reproduce by 

 means of eggs, from which develop free -swimming embryos, 



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