EPITHELIOID MEMBRANES IN MONAXONID SPONGES 553 
over the margin in the shape of a thin film. This gradually 
spreads across the pore becoming a well marked pore membrane. 
As it spreads the originally marginal nucleus passes into it. The 
sketches (fig. 10) show successive stages in the passage of the 
membrane across the pore. At 9.58 the pore canal is almost 
completely closed in. Its outline is still distinct at this time. Five 
minutes later the pore is completely closed, and the outline of 
the pore canal is no longer distinguishable. 
Pore 2. The pore at 10 a.m. is partly closed by a few intercon- 
nected strands of protoplasm which include a nucleus (fig. 12). 
The strands are thin and delicate, and are in continuity with the 
surrounding epidermis. The protoplasmic strands change form 
and arrangement, and the nucleus shifts its position, all very 
quickly. Such amoeboid movements continue for some minutes. 
During their progress camera sketches were made, and the con- 
ditions at 10.05 and 10.07 are shown in fig. 12. By 10.10 the 
protoplasmic strands have taken the shape of a marginal film. 
This is drawn into the epidermis, the nucleus remaining at the 
margin of the pore, and at 10.12 there is only the usual appear- 
ance of an open pore. The nucleus now shifts quickly back and 
forth along the margin of the pore, narrow marginal films appear- 
ing and disappearing as the nucleus changes position (comp. 
sketches drawn at 10.15, 10.17, 10.20, fig. 12). The narrow mar- 
ginal film present at 10.20 begins to spread at 10.21 and rapidly 
covers the whole pore, becoming a pore membrane into which the 
nucleus passes. Two stages in the completion of the pore mem- 
brane are drawn as they appear at 10 . 23 and 10.25. The pore is 
completely closed by 10.27. The wall of the pore canal was dis- 
tinct all round until 10.21. Shortl}^ after that time it began to 
grow indistinct round a part of the circumference (right side). 
At 10.25 it was no longer distinguishable in this region and was 
only vaguely outlined on the opposite side. The pore canal was 
kept under observation until 10.40 a. m. At that time its outline 
(p.c. in fig. 13) was still vaguely distinguishable, although cir- 
cumscribing a much smaller area than formerly. 
Fore 3. When the observations began the pore canal (fig. 14, 
1.45 p. m.) was far smaller than the normal. It had evidently 
