THE SPONGES— PHYLUM PORIFERA 



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products of the sponge seem to be repulsive to many forms of animal life 

 and thus excretion becomes a form of protection from possible enemies. 

 Reproduction may be by two methods. The first is by budding 

 and does not involve any union of gametes to form a zygote ; so we may 

 speak of it as asexual, meaning without sex. In this method a little bud 

 appears near the base of an adult sponge, and this gradually grows to 

 form a full-sized scypha. It may continue to adhere to the parent after 



Courtesy General Biological Supply House 



Fig. 8.2. Spicules of scypha. These calcified structures are distributed throughout 

 the softer body parts for the purpose of support and protection. 



reaching full size, and frequently colonies of many individuals may be 

 seen that have arisen from one through budding. Sometimes they break 

 off from the parent and form a new attachment, thus starting a new 

 colony. 



In sexual reproduction certain cells of the body become differentiated 

 into sperms while others form eggs. As is true in all cases of sexual re- 

 production, many more sperms are formed than eggs, since the egg has 

 to be larger in order to store food for the developing embryo, while the 

 sperms need only food enough to enable them to swim to the egg. 



