THE OOLLAR-CELLS OF HETEROCGLA. Ad 
hours in sea water after gathering. Very satisfactory preparation; all over it 
could be seen tall cylindrical cells, wide apart, with stiff cylindrical collars and 
flagella very active until two and a half hours after the preparation was made. 
These cells drawn in the first half-hour. Part of the same sponge placed 
when this preparation was made into osmic acid for an hour and a quarter, 
and dialysed through alcohol and benzol, showed in sections stained on the 
slide spherical or oblate collar-cells with a flat Sollas’s membrane and few 
flagella (possibly due to imperfect dialysation in benzol). 
Fie. 5.—From same sponge as fig. 19, six hours in a small saucer of sea- 
water; flagellar movement languid. 
Fic. 6.—S. compressum, flagella moving. 
Fic. 7.—S. compressum. Edge of collar showing beaded or milled-edge 
appearance, flagellum in optic section ; same preparation as fig. 5. 
Fic. 8.—S. compressum, living section; a, soon after the preparation 
was made; 4, twenty minutes after, the flagella in very violent action; c, one 
hour forty minutes after (the two left-hand cells of 4), the right flagellum 
was gone, the left still working; ¢, two hours twenty minutes after, the tops 
of the same cells, the bodies being hidden. Flagella were still moving in 
many of the chambers two hours thirty-five minutes from the time the prepa- 
ration was made; many of the collar-cells were elongated to six or seven times 
their width. 
Fic. 9.—T wo successive drawings of a cell from the same sponge as fig. 4, 
but an hour and a half after the preparation was made. Part of the section 
was dead; the flagellum of this cell was moving well. Note the very long 
collar. 
Fics. 10 and 12.—S. compressum gathered under a moist rock, placed 
for three hours in the circulation of the Biological Station. The first drawings 
from the living section present nearly the same appearance as fig. 1, the cells 
being short and more closely packed than usual. After three quarters of an 
hour the appearance is much as in fig. 8a, and the flagella are growing slack. 
Fig. 10 was drawn one hour and twenty minutes, and fig. 12 one hour and 
fifty minutes after preparation; the flagella were still moving in fig. 10, 
motionless in fig. 12. No further change was observed two and a quarter 
hours after preparation. Paraffin sections formed Series C of the text. 
Fic. 11.—S. raphanus, some time under the cover-slip. There were 
flagella still moving in the preparation, though there were none visible on the 
cells drawn in 4 and ec. 
Fie. 12.—See fig. 10. 
Fic. 13.—S. compressum, ten hours in sea water after twenty-seven 
hours absence from it; flagella moving actively. This is the typical form of 
cell, though there are a few with collars of the normal form. As noticed also 
