PHYLUM P0R1FEE.A 



123 



may be contractions of the entire body. These movements are 

 accomplished by individual contractile cells. These reactions may 

 involve the entire body, or they may be local. Laymen and many 

 zoologists think of sponges as sluggish, inactive forms, because 

 they are sessile. On the contrary, these ajiimals work day and night 

 to keep a continuous current of water to supply their vital needs. 

 It is reported that an average sponge will pump approximately 

 forty-five gallons of water through his body in forty-eight hours. 

 Activities and coordination in Scypha and sponges generally are 

 quite limited by lack of a nervous system. Individual cells respond 

 directly to stimuli, and impulses are conducted simply from cell to 

 cell in a primitive fashion. This results in very slow transmission 

 of impulses and is called neuroid transmission. 



External Anatomy 



The average length of Scypha is about three-fourths of an inch. 

 It is rather goblet-shaped with the excurrent opening, osculum, at 

 the top. A row of picketlike spicules or spines encircles the osculum, 



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Fig. 51. — Scypha coronata (Grantia), showing habit of life. 



