224 W. G. RIDEWOOD. 



The relation wliicli tlie collar region^ as dissected out, bears 

 to the whole bud will be made clear by reference to text- 

 fig. 5, A, a diagrammatic side view of a bud with three pairs 

 of plumes, and text-fig. 10, a diagram of a longitudinal 

 section of the adult polypide; in the latter figure the limit 

 of the collar region is marked by two lines of heavy dashes. 



The results here recorded and illustrated are based upon 

 135 preparations of buds made and mounted as above ex- 

 plained. In some cases (e.g. text-fig. 6, p) the three parts — 

 " body," collar appendages, and shield — were drawn sepa- 

 rately on tracing paper, and the perfect bud was recon- 

 structed by a superposing of these transparent sheets. 



No staining fluids were used. The dissections were made 

 under a Greenough binocular erecting microscope magni- 

 fying 20 and 40 diameters ; the drawings were made by the 

 aid of a compound microscope with Zeiss apochromatic 8 mm. 

 objective and No. 6 compensating ocular with eye-piece 

 micrometer. The figures in text-figs. 2, 3, 4, C, 7, and 9 are 

 all reproduced to the same scale of enlargement, viz. 62 

 diameters. 



Development of the Plumes in Buds of Cephalodiscus 



hodgsoni. 



In the earliest phase of development the bud is ovoid or 

 pyriform (text-fig. 2, a) without signs of buccal shield or 

 plumes. The shield and the first pair of plumes make their 

 appearance simultaneously (b and c). The plumes are at first 

 small mounds, later hemispherical (d), and still later longer 

 than broad (e, p, etc.). The second pair of plumes appear 

 on the external side of the first pair (d, 2), and in contact 

 Avith them. The two plumes of the first pair are not in con- 

 tact with one another at their bases. The third pair of 

 plumes appear lateral to the second pair (k, 3), and in con- 

 tact with them. 



The l)ud increases considerably in size before the fourth 



