PLATE V. 



Fio-. 1. Tip of oue of the plumes of the polypide of Cephalodiscus, showing the 

 glandular uaturc of the enlarged region. The filaments (/) have been turned 

 to the left ; ca, central axis of main stem ; hp, hypodcrm. The longitudinal 

 fibres running alonsr the axis are observed to the left as well as over the 

 axis ; x 210. 



Fig. 2. Portion of the middle of a plume with the bases of the filaments {/), viewed 

 laterally, after the action of a dilute solution of potash. The skeletal axis is 

 observed in the centre of each filament, and as this skeletal axis {sk) widens 

 out at its base, the double outline at each side is well marked ; ca, central 

 axis of main stem, with its longitudinal fibres ; x 350. 



Fig. 3. Transverse section of a young bud on the appearance of the first two lophophoral 

 processes or plumes (Zp) as two rounded bosses composed of tissue resembling 

 hypoderm. The buccal disk [hd) is cut at its anterior region, but the central 

 space {he) of the organ is well developed. The collar space {yc) is com- 

 paratively large at this stage, and lies close beneath the nerve-centre ; x 350. 



Fig. 4. Transverse section of the terminal region of the body-cavity of an older bud 

 than the foregoing, the tip of the alimentary canal {al) being left as a thin 

 plate in the centre, and bound dorsally and ventrally l^y the median 

 mesentery (wis). The great longitudinal muscle is cut near the commence- 

 ment of the pedicle, and already shows the double ventral curvatures so 

 characteristic of the latter ; ht, basement-tissue ; co, the body-cavity ; x 350. 



Fig. 5. Ovum on its escape from the adult ; ec, egg-capsule ; ov, ovum proper ; st, 

 stalk; x90. 



Fig. 6. Outline of another ovum in which the yolk is ovoid, instead of circular as in the 

 former case ; x 90. 



