54 



W. G. RIDEWOOD. 



Buccal Shield. 



The shield of the adult polypide of 6'. /lodrjsoni varies in size, but on an average 

 of a great many cases measures 1 • 2 by 1 ■ 2 mm. (text-fig. 17, E). The antero-posterior 

 diameter, however, may be as much as -2 or -3 mm. longer or shorter than the 

 maximum width, the organ being evidently capable of great contortion in all 

 directions. The posterior lobe is equal in width to the front lobe, or is slightly 

 less ; the centre of the red line is about four-fifths or five-sixths of the antero-posterior 

 diameter from the front edge. The diagram given in text-figure 17, E is a composite 

 figure of about twenty specimens. 



Text-Figure 17. — A = Buccal shield of a bud of C. Iwdgsoni with two pairs of plume-axes only. B = Shield of a bud 

 with the fourth pair of plume-axes making their appearance as hemispherical projections. C = Shield of a bud 

 with the fifth pair of plume-axes making their appearance as hemispherical projections. D = Shield of a bud with 

 the sixth i)lume-axes about twice as long as broad, and without pinnules. E = Shield of adult polypide of 

 C. hodgscmi. P = Shield of adult polypide of C. dodecalophus. These six figures are drawn to the same 

 scale (x 40). 



The red line makes its first aj^pearance in the bud at a time when the fourth 

 plume-axes have the form of hemispherical prominences at the base of the third pair. 

 It is at this period only a short line extending across not more than one-third or 

 one-half of the total width of the shield (text-fig. 17, B), and it is in this stage 

 and for some time later relatively more remote from the posterior edge of the shield 

 than it is in the adult {cf. text-fig. 17, B, C, D, E) ; the posterior lobe does not 

 enlarge quite so rapidly as the anterior lobe as growth proceeds. Until the stage 

 at which the fifth pair of plume-axes normally make their appearance — they are in 



