CHAPTEE IV 

 PHYLUM III.: PORIFERA (Sponges) 



In Sponges the body is composed of many cells lying in 

 close contact with one another, and usually forming a yellow- 

 ish asymmetrical mass of varying size, which is fixed to a 

 rock or seaweed, and which is practically motionless, though it 

 may shrink slightly if touched ; if squeezed, it is found to be 

 compressible and yet tough, regaining its former shape when 

 the pressure is removed. The surface of the sponge is dotted 

 over with minute- pores, and one or more larger openings 

 known as oscula also occur. Sponges live always submerged 

 in water, and if a few grains of some pigment such as 

 carmine are dropped in the water near them, it will be seen 



that the grains are drawn 

 into the minute "inhalent" 

 pores, and also that they are 

 driven away from the larger 

 "oscula." This current of 

 water is produced by the 

 lashing of the protoplasmic 

 threads or flagella, possessed 

 by certain of the cells within 

 -q' ' the body (see Fig. 27), and it 



Fig. 25.— The Purse Sponge (Grantia carries into the body both 



comprcssa) (natural size), attached the oxygen necessary for 



to a branch of seaweed. • i.- j i ii 



respiration and also the 



0, Oscula. T . 



decaying organic matter 

 which probably serves as food. 



The form of the body varies very much. Sometimes it has 

 the shape of a little flattened bag, with usually one osculum 

 only, as in the Purse sponge, Gh-antia compressa (see Fig. 25) ; 



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