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 



Siphonin tulipa, auct. (after Zittel). A, a vertical section of the body, natural size, showing 

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

 excurrent canals. B, 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. 28. 



A, Setidium obtectum, O.S., 5. L, Colinella inscripta, O.S., f. (Both after Agas.siz.) 



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, 



