SPONGES 



ramifying only in one plane, from which arise erect diverticula at 

 intervals which acquire oscula at their extremities, and thus assume 

 the characters of new individuals. In the arborescent forms, on 

 the other hand (Fig. 4), the erect oscular tube sends out numerous 



FIG. 2l>. 

 Vetulina stalactites, O.3. (After Agassiz). j. 



diverticula along its whole length, which form new oscula at their 

 extremities when still quite short, and the daughter individuals 

 which are thus formed repeat the same process, throwing out 

 diverticula rapidly on every side. In this way arises an arborescent 



FIG. 30. 



A, Tethya lyncitrium, L., natural size. At the summit is seen the partially retracted 

 osculum. Jl, section across Tuberella sp., showing the thick cortex and the radial arrangement 

 of the body skeleton. 



Ascon colony which creeps over the seaweeds like a climbing plant, 

 attaching itself at intervals by direct contact. Among the Hetero- 

 coela, also, erect arborescent colonies are not uncommon, and in 

 Leucandra aspera (Fig. 12) rapid growth and budding may lead to 



