PLUMES OF CEPHALODISCUS. 



225 



plumes appear ; the buccal shield assumes its definitive shape 

 by becoming flattened^ and by the differentiation of the pos- 



^-b.s. 



Text-figuke 2. — Oeplialodiscus liodgsoni. I'iguies illubtratiiij,^ 

 the development of the plumes of the buds. C and L are side views, 

 the otliers are dorsal views. J represents the collar and its appendajres 

 (plumes and post-oral lamella) dissected from a bud a little older than li. 

 The first pair of plumes are just appearing in B and C, the second in 

 D, the third in E, the fourth in II, and the fifth in K and L. The 

 series is continued in text-fig. 3. All figures enlarged G2 diameters. 

 For explanation of the lettering see end of paper. 



terior lobe. In G and h the dotted line marks the position 

 of the free edge of the posterior lobe. The fourth plumes 



