CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF 

 THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 

 COLLEGE. — No. 236. 



THE STRUCTURE OF THE GORGONIAN CORAL 



rSEUDOPLEXAURA CRASSA WRIGHT 



AND STUDER.i 



By Wayland M. Chester, 

 Presented by E. L. Mark, March 12. 1913. Received April 5, 1913. 



CONTENTS. 



Introduction 

 Methods . . . 

 General structure 

 Ectoderm . . , 



... 737 



... 740 



... 740 



... 747 



Mesogloea 751 



Eiuloderm 754 



Structures concerned in nutri- 

 tion 757 



Dorsal mesenterial filaments 759 



Growth 760 



Muscles and nerves .... 760 



Skeleton and axis epithelium . 762 



Summary 768 



Bibliography 770 



Explanation of plates . . , 773 



Introduction. 



PsEUDOPLEXAURA CRASSA is found on the reefs of Florida, of the 

 West Indies, and of the Bermuda Islands. It is very abundant in 

 the siiallow water of the inner reefs of Bermuda, and is there one of 

 the two or tlu-ee very common sea whips; but it is found in the deeper 

 waters of the outer reefs as well. The range in depth, to include the 

 greater number of colonies, is from a position near the surface at low 

 water to seven or eight meters. 



Ellis and Solander (1786) described this colony under the name of 

 Gorgonia crassa. KoUiker (1872) placed under the name of Plexaura 

 branched, sea-rod forms in which the polyps completely retract into a 

 comparatively thick coenenchyma, in which club-shaped and spiny 

 spindle-shaped spicules appear. The different species were divided 

 into two groups: Plexaura durae and Plexaura molles. Hargitt 

 and Rogers (.-01, p. 2So) follow Verrill ('65, p. 34) in describing this 

 form as Plexaura crassa. Wright and Studer ('89, p. 141-143), from 

 observations of Bermuda specimens, created for this species a new 



1 Contributions from the Bermuda Biological Station for Research. No. 27. 



