i8 



SPONGES 



distinguished. In the simplest cases the new oscular tubes arise 

 from tlie tubar system by the side of the parent individual, and the 



B 



Fio. 27. 



Siphonia tulipa, aiict. (after Zittel). A, a vprtical section of the body, natural size, showinn 

 the small gastral cavity, the radially directed incnrrent canals, and the concentrically disposed 

 excurrent canals. H, the entire sponge, half natural size. 



colony assumes a compact or bushy form (Fig. 3), which may take 

 on a spreading or an arborescent growth by variations in the mode 



Fig. 2S. 

 .-), Setidium obtcctum, (».S., g. /;, O'linelln ins<-ripta, O.S., 3. (Both after Agassiz.) 



of budding. In the spreading fiirms (Fig. 5) the diverticula at the 

 base of the sponge person come into contact with the substratum 

 and grow to a great length, forming a stolon-like basal network, 



