PLATE XXVIII . 



Figs, io to 19^. Rkizomolgula arenaria. 



10. Habit sketch. Natural size. The method of drawing makes it impos- 

 sible to successful!}' show the sand on the surface. 



11. Left side of animal dissected from the test. The stomach (5/".) with 

 its well-defined ribs is shown, as is also the peculiar coiled-up condition 

 of the material within the intestine. 



12. View of orifices of anterior end with test removed. 



13. Portion of peduncle (-P. ) with numerous rootlets, some showing the 

 bulbous terminations (r. 3.). (X 15)' 



14. Magnified view of main stem of peduncle (Z'. ) with a single rootlet 

 {r. A) arising from it. This shows its single muscle fiber {m. f. ) con- 

 tinuing up into the peduncle. 



15. Branching rootlet showing how the single muscle fiber of the ultimate 

 rootlet (r. t.) reaches into the larger portion of the branch. 



16. Optical section of portion of a peduncle ; its outer edge marked by the 

 test {tst.); bundle of muscle fibers {m. b.). A single muscle fiber [m. 

 f.) is separated from the general mass and is clearly seen imbedded in 

 the test with test cells {tst. c.) entirely surrounding it. 



17. Similar to last but more clearly showing the tendency of the test cells to 

 become elongated. 



18. Portion of branchial sac showing four folds ( f-f-^f-'^f-^)- The folds 

 f.^ and/!^ a^e spread apart to bring out the infundibula; and the inter- 

 nal longitudinal vessels confined to the folds. 



19. Portion of peripharyngeal field. 



19^. Small piece of mantle showing the papillae. 



19^. One of the papillae, magnified, showing its wall and lumen. 



(262) 



