157 
the breadth of the single cells is limited, though variable, 
makes it a necessity that at different times new series of zocecia 
become interpolated, the colony otherwise acquiring a lobed 
outline. This interpolation of a new series of cells or zocecia 
is effected in this way, viz., that a zocecium instead of pro- 
ducing one zocecium at its anterior edge produces two, both 
of them originating from an at first simple bud—a common 
bud, by secondary division. ‘The same process often takes 
place when in an arborescent colony a twig dichotomizes. 
That a “common bud” is produced by two or more mother 
cells, or by the margin of the whole colony, I never was able 
to observe, and it is also difficult to agree with this doctrine 
from a theoretical point of View, since it is quite incompatible 
with the scientific conception of the individual in so highly 
organised a class, that many of them should unite to the pro- 
duction of one bud in common. 
A careful examination of many colonies of Flustra mem- 
branacea! gave me the conviction that also in this species a 
“common bud,” in the meaning given to this designation by 
Smitt, does not exist. 
The increase of the colonies of Flustra membranacea during 
the summer is a very rapid one, and the growing margim 
shows a very peculiar appearance. A marginal zone, of 
sometimes an inch in breadth, contains not fully developed 
zocecia, but only more or less immature ones. The imma- 
ture cells, which are nearest to the centre of the colony, are 
principally distinguished by the more imperfect calcification 
of the ectocyst, and the smaller size of the polypides. The 
still younger and more eccentrically situated cells do not 
show any calcification at all, the two posterior spines of the 
cell are represented only by small rounded knobs, and the 
opercular opening in the ectocyst not yet opened, and conse- 
quently the very small polypides are not yet able to become 
protruded. In the last zone of distinct cells every zocecium 
consist of a quadrangular depressed bag surrounded by a 
tough chitinous membrane lined with a layer of cells, and 
showing at its posterior wall a small knoblike polypide bud. 
' Smitt gives in his admirable paper, “ Kritisk forteckning Ofver Skan- 
dinaviens Hafs-Bryozoer,” ‘ Oefversigt af Kongl. Vet. Akad. Forh.,’ 1867, 
No. 5, p. 357, the following diagnosis of this species : 
Fl. membranacea (Lin. Sol.). 
Char.—Colonia in crust formam expansa zoccia ad angulos distales 
(i.e., juniores exteriores) seta brevi mucronata praebet. Avicularia et ocecia 
desunt. 
But I have satisfied myself that the two spines Smitt attributes to the 
es part of the cell belong really to the proximal, 7.¢., the older part of the 
cell. 
