PLUMES OF CEPHALODISCUS. 221 



On the Development of the Plumes in Buds of 

 Cephalodiscus. 



By 



W. CJ. Ridcwood, D.Sc, 



Lecturer on Biology at St. Mary's Medical Scliool, University of London. 



Witli 11 Text-fiirures. 



PAGE 



Introduction ....... 221 



Methods . . . . . . .223 



Development of the Plumes in Buds ol' Cephalodiscus 



liodgsoni ...... 224; 



Development of the Plumes in Buds of Cephalodiscus 



dodecalophus . . . . . 230 



Development of the Plumes in Buds of Cephalodiscus 



nigrescens . . . . . . 235 



Development of the Plumes in Buds of Cephalodiscus 



gilchristi ...... 242 



General Remarks on the Collar and its Appendages . . 245 



Summary ....... 251 



Explanation of the Abbreviations employed in Text-ligures 2, 



3, 4, 6, 7, and 9 252 



Intkoduction. 



During the progress of an investigation on the anatomy of 

 three recently discovered species of Cephalodiscus (C. 

 nigrescens, C. hodgsoni, and C. gilchristi), kindly 

 entrusted to me for description by Prof. E. Ray Lankester, 

 F.R.S., Director of the Natural History Museum, Loudon, I 

 noticed that in the development of the buds there is no 

 torsion of the first and second plume-axes such as is de- 

 scribed by Masterman as occurring in buds of C. dodeca- 



