138 
MURIEL ROBERTSON. 
EXPLANATION OF PLATE 19, 
Illustrating Miss Muriel Robertson’s paper on “The Division 
of the Collar-cells of the Calcarea Heterocoela.” 
[The figures are drawn with the aid of the camera lucida at a uniform 
magnification of 2000 linear. 1 ] 
Fig. 1. — Collar-cells of Grantia showing the flask shape. Note the 
karyosome in the nucleus. 
Fig. 2. — Collar-cells of Grantia showing the elongated chimney 
shape. 
Fig. 3. — Collar-cell with reticulate nucleus. It also shows the double 
rhizoplast forming the connection between the blepharoplast and the 
nucleus (Grantia). 
Fig. 4. — Collar-cell of Sycon showing pale nucleus with deeply 
staining karyosome. 
Fig. 5. — Collar-cell of Grantia showing reticulate nucleus with 
karyosome. Note the double rhizoplast. 
Fig. 6. — Early spireme-stage (Grantia). 
Fig. 7. — Stage very like that shown in fig. 6, but the spireme is in a 
still earlier condition (Grantia). 
Fig. 8. — Precocious division of the blepharoplast ; the specimen is 
fixed with Flemming’s solution (Grantia). 
Fig. 9. — Early stage in division ; the blepharoplast is newly divided, 
and the spireme is just being formed at the expense of the karyosome. 
The flagellum has been thrown off (Sycon). 
Fig. 10. — Slightly later stage ; the blepharoplast has divided but the 
flagellum is still retained (Sycon). 
Fig. 11. — Slightly aberrant stage ; the blepharoplast - centrosomes 
occupy either end of the spindle which is just forming, while the spireme- 
stage has not yet been completed (Grantia). 
Fig. 12. — Equatorial plate-stage with the chromosomes just splitting. 
The first rudiment of the new flagellum is visible at one pole 
(Grantia). 
Figs. 13 and 14. — Equatorial plate-stages (Sycon). 
Fig. 15. — Equatorial plate showing flagellum growing out from either 
centrosome (Sycon). 
1 I am indebted to Miss Mabel Rhodes for the care and skill with 
which she has executed the figures. 
