SMITHSONIAN INSTITUTION 



PLATE C 

 Further Stages in Development of Comactinia 



PAGE 



Figs. 1-7. Comactinia meridionalis (A, and E. C. Agassiz) 83 



Figs, ia, b. Incipient cirral stage. Orals form a low pyramid around the mouth, separated by 

 perisome both from basals and radials ; short stumps of cirri appear upon the proximal 

 columnal. X 20. 



20, b. Specimen further advanced, with strong cirri and smaller orals ; basals are now small 

 plates lying almost flat. X 20. 



30, b. Pinnule stage. Visceral mass, greatly enlarged, enclosed by finely plated perisome, with 

 orals reduced to small triangular plates surrounding the mouth, from which well 

 defined ambulacra pass to the arms ; basals have entirely disappeared, and radials are 

 nearly horizontal. About the end of the " pentacrinoid " stage. X 15. 



4. Comatulid stage. Stem has been cast off; basals are fused into the centrodorsal, or 



" Rosette " ; the radianal, now separated from the radials, is in process of resorption 

 along with the interradials from which it scarcely differs. The cirri beyond their bases 

 are omitted in the drawing. X 12. 



5. Tegmen of an adult specimen, consisting of the granular skin, subcentral anal tube, exocy- 



clic mouth with asymmetric ambulacra both permanently displaced by pressure of the 

 rectum; orals have entirely disappeared. X 5. 



6. Migration of the radianal. Diagrammatic figure based on fig. la, with dotted line showing 



course of the plate in the successive larval stages here illustrated, from primitive 

 position under the right posterior radial to the left and upward until eliminated from 

 the calyz. X 20. 



7. Fragment of cirrus showing attachment of two " pentacrinoids " by the flattened base of 



the stem. X IS- 



