HIGH SCHOOL ZOOLOGY, 



249 



7. By many zoologists the Porifera or Sponges are regarded 

 as Coelenteiates, chiefly distinguished by the absence of thread- 

 cells ; they have so many other peculiarities, however, that it is 

 convenient to consider them apart. Although one family 

 [Spougillidai) is confined to fresh-water, and is abundantly 

 represented in our lakes and streams (Fig. 186), yet it does not 



Fiy:. 184. — Org-anpipe coral. 



(Tubijiora )nunica.). 



Some of the polyps are e.^cpanded. 



Fig. 185. — Michclinca convexa. 

 Devonian. 



Fig. 186. — Spongilla laemtris. 



contain conspicuous forms, and the word " sponge " is most fre- 

 quently connected with the marine animals, whose skeletons we 

 use in every day life. Yet those are derived from but one 



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