ON THE DEVELOPMENT OF LICHENOPORA VERRUCARIA. 87 
occlusion of the fertile zowcium. This process is not 
easy to see in a colony which is resting in its position of most 
stable equilibrium on its flat surface; but it can be seen 
without difficulty in a colony of suitable age which has been 
mounted on a rotating cylinder in the manner described on 
p- 74. No general rule can be laid down with regard to the 
size of the entire colony in its relation to the closure of the 
ovicell. The smallest colony in which I have found this 
process actually beginning measured ‘77 mm. in diameter, 
while the largest colony in the same condition as regards its 
ovicell was 1:13 mm. across. In nearly all the cases I have 
actually observed at this stage, 2? was the fertile zocecium, 
although this rule is by no means invariable. A reference to 
the woodcut on p. 78 will show that the orifice of 2? may be 
described as having an axial and an abaxial side. The occlu- 
sion of the zocecium commences with the formation of a calca- 
reous film, starting from the abaxial edge of the zocecium. 
This film grows inwards as a cap to the zocecium (fig. 18) ; 
but while it is closely fitted on to, and indeed arises from the 
abaxial edge of the orifice, it grows over the axial side of the 
edge as an arch which does not fuse with the edge. The film 
is the beginning of the roof of the ovicell; and it is clear 
from fig. 13 that a passage leading from z? into the cavity of 
the ovicell is left between the calcareous film and the axial 
side of the edge of the orifice of z2. Through this passage 
the embryo passes from the fertile zowcium into 
the ovicell. It should perhaps be pointed out that this 
statement is to some extent a matter of inference. I cannot 
claim to have first found this passage in a particular colony, 
and then to have observed the embryo on its way through the 
passage. But I have been able to show that the embryo 
actually passes from the fertile zocecium into the ovicell 
through an aperture close below the roof of the latter; and it 
may fairly be concluded that the passage whose formation we 
have just considered is really formed for this purpose. 
No sooner has the fertile zocecium been occluded than the 
formation of the orifice of the ovicell is commenced. This is 
