i8 



SPONGES 



distinguished. In the simplest cases the new oscular tubes arise 

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



B 



Fio. 27. 



Siphnnifi tidifKt, anct. (after Zittel). A, a vertical section of the Ixxly, natural size, showing 

 the small Austral cavity, the radially directed incnrn-nt canals, and the 'concentrically disposed 

 exeurrent canals, li, 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 



FlO. 28. 

 A, Setidium obtectum, OS., 3. /?, CoIineUa inscripta, O.8., |. (Both after Agassiz.) 



of budding. In the spreading forms (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, 



