CEPHALODISCUS. 65 



EXPLANATION OF THE PLATES. 



PLATE 1. 



Photograph of Gephalodiscus {Idiothecia) nif/rescens ; natural size. (From Lankester, 15.) 



PLATE 2. 



Fig. 1. — Photographic reproduction of Cephalodkcus (De)niofhecia) hod'/soni ; natural size. A, small perfect 



specimen ; B, larger specimen with the tips of the spines shrivelled, owing to drying. 

 Fir. 2. —Photograph of a massive colony of C'ephalodisciis {Tdiothecia) niffrescens ; natural size. 



PLATE 3. 



Fig. 3. — Ce])halodiscns (Tdiothecia) nigresceiis, drawing of a branch as seen against a white background. 



(X li.) 

 Fig. 4.— Median longitudinal section of same, (x li.) In figs. 3 and 4 the black parts are the 



polypides seen through the transparent test ; the small white ovals are free ova in the tubes. 

 Fig. 5. — Drawing of an older branch, (x li.) a, h, c, scars left by fallen branches. 

 Fig. G. — Transverse section of a branch, (x li.) 

 Fig. 7. — A polypide of C'eplialodiscus nigrescens as it appears on removal from its tube, (x 13.) 



hA, bud flattened against the ventral side of the polypide; //.2, bud flattened against the 



far side of the polypide ; li.?>, five other buds ; h.s., buccal shield ; go., gonad ; |>/., plumes ; 



St., stolon ; v.m., visceral mass. 

 Fig. 8. — A polypide of C. nigrescens with plumes more expanded and with the buds disentangled. 



(X 13.) h., buds; other letters as in fig. 7. Figs. 7 and 8 were drawn under a Greenough 



binocular microscope, with a strong top illumination ; the polypides do not look as black as 



they would if the illumination had been less intense. 

 Fig. 9.— Cells of the pigmented epithelium as they appear when teased out and examined in dilute 



glycerine. 



PLATE 4. 



YiQ. 10. — Diagram of a longitudinal section of the distal half of a branch of Cephahdiscus {Tdiothecia 

 nigrescens) showing the relative lengths and curvatures of the various tubes, (x 2.) In this 

 diagram the whole of the tubes visible are represented as lying wholly in the radial plane ; as a 

 matter of fact the inner ends of the tubes twist about one another in the axial part of the 

 branch (see fig. 4, pi. 3) Tlie poly]3ides are not shown. 



Fig. 11. — Diagram of one of the tubes of C. nigrescens, with a contracted polypide within, showing 

 the form of the lip of the tube and the hemispherical septa at the blind end. The ragged 

 edge of the figure represents the irregular surface left after picking away the adjacent 

 tubes, (x 8.) 



Fig. 12. — Longitudinal section of the mouth of a tube of G. nigrescens taken through the middle 

 of the Up, showing the mode of deposition of the layers of the test, (x 15.) 



Fig. 13. — The distal end of a long uninhabited tube, dissected out and cut longitudinally. Note the 

 six irregular closing septa, and the close-set superficial layers of common soft test burying the 

 mouth of the tube, (x 15.) 



Fig. 14.— Polypide of C. nigrescens found free, i.e., not in a tube. The buds have been cut 

 away, (x 14.) 



Fig. 15. — A polypide of C. nigrescens taken from one of the short terminal tubes of the branch, (x 11.) 

 In figs. 14 and 15 the blackness of the polypides has been reduced in order to show the shape 

 of the body ; were this not done the body would appear almost as a silhouette. 



