author's abstract op this paper issued 

 by the bibliographic service, february 3 



THE ORGANIZATION OF RENILLA' 



G. H. PARKER 



ONE FIGURE 



The curious sea-pen Renilla is a most favorable form in which 

 to study colonial organization, for the relatively large size of its 

 autozooids and its complete and natural freedom from attach- 

 ment make it an unusually satisfactory organism for experi- 

 mental study. The species upon which the work recorded in 

 this paper was done was Renilla amethystina Verrill from the 

 coast of Southern California, and I am under obligations to the 

 staff of the Scripps Institution for Biological Research at La 

 Jolla for many courtesies while I was carrying on this work. 



Renilla is unlike other pennatulids in that its rachis, instead 

 of being elongate, is expanded into a broad heart-shaped or kid- 

 ney-shaped disc, only one surface of which carries zooids. The 

 peduncle is a fleshy tail-like extension and is peculiar in that it 

 is without an axial skeleton. In Renilla amethystina the ex- 

 panded rachis may measure as much as 6 or 7 cm. in breadth and 

 may carry several hundred autozooids and many more siphono- 

 zooids. The peduncle, when distended, may reach the length 

 of 5 to 6 cm. Some confusion exists as to the terminology used 

 for the surfaces of Renilla. In the conventional system employed 

 for pennatulids the face corresponding to that on which the 

 zooids are borne in Renilla is known as the ventral face and the 

 opposite as the dorsal one. As Renilla rests on the sand in 

 natural position the upper face is what according to this system 

 would be called ventral, hence this condition has led to some 

 confusion in terminology, for not a few authors have naturally 



1 Contributions from the Zoological Laboratory of the Museum of Compara- 

 tive Zoology at Harvard College, No. 316. 



499 



