Plate 50 



Fig. 1. Theonclla cylindrica. Phyllotriaenes. a, cladoine from above ; b, cla- 

 doine from below. X150. 



2. Theonella cylindrica. Part of tbe desmal framework. X230. 



3. Theonella cylindrica. Young desma, from periphery of sponge ; clads 



breaking up terminally into short branches which bear the irregular 

 tubercles of zygosis. X230. 



4. Jereopsis fruticosa. Small free amphitriaenes from the ectosome. In 



one of the spicules drawn, the axial canal could not be distinctly 

 traced at one end of the spicule. X150. 



5. Jereopsis fruticosa. Young desma with simple clads from ectosome, 



after treatment with hydrofluoric acid which has somewhat cor- 

 roded the spicule. X150. 



6. Jereopsis fruticosa. Streptasters. a, amphiaster from interior ; o, 



amphiaster from interior approaching the spiraster type ; c, spiras- 

 ter from dermal surface. X620. 



7. Jereopsis fruticosa. An uncorroded and nearly perfect desma detached 



from the skeleton in sectioning ; a bit of an adjoining desma in 

 zygosis is also shown. X150. 



8. Costifer ra si for mis. Rare types of desma; main axis bearing a clad 



or a few clads; articular facets on epirhabd only. X45. 



9. Jereopsis fruticosa. Skeletal desmas isolated with hydrofluoric acid 



and therefore corroded. The two sets of clads at opposite ends 

 of the shaft may be about equally developed, as in a. Or the clads 

 at one end are much more extensively developed than at the other 

 end, as in b and c. X1S0. 



10. Coscinospongia thomasi (Sollas). Part of a developed desma. X220. 



11. Jereopsis fruticosa. Dichotriaenes. X150. 



12. Jereopsis fruticosa. One end of a fully developed uncorroded desma 



forming part of the skeletal framework, a is the shaft. Of the 

 three primary branches into which it breaks at this end, only one 

 is covered with the tubercles of zygosis. The middle primary branch 

 divides into three secondaries. The middle secondary divides into 

 two tertiaries, one of which, x, ascends to pass into a skeletal node 

 at another level, n, a skeletal node as seen at a single focus; the 

 entire node is much more complex, several desmas interlocking to 

 form it. X210. 



13. Costifer vasifomUs. Common types of desma, rod-like and with 



out clads. n, and b, still interlocking, each with two facets; c, 

 with ends that are somewhat gnarled. X45. 



14. Costifer vast for in is. a. oxea ; b. plagiotriaene. X45. 

 520 



