552 
H. V. WILSON 
split and mounted in water, glycerine, and balsam. Tangen- 
tial sections were also made. As a control pieces of an expanded 
Leptogorgia were used, and the epithelial cells on the surface of 
the polyps were here outlined with great distinctness. 
Pores, pore canals, and pore membranes 
In the preparations made from preserved material, the pores 
are sometimes wide open or partially, sometimes completely, 
closed by pore membranes. The pore membrane as in Stylotella 
is simply an extension of the epidermis. When it incompletely 
closes the pore it has a single nucleus (fig. 11,), and even when 
it is complete it may have but one (fig. 11,). Frequently, how- 
ever, when it is complete it exhibits more than one nucleus (fig. 
11, 6). As long as the pore membrane is imperfect the outline 
of the pore canal is distinct. When the pores are completely 
closed however it often happens that the outline of the pore canal 
is vague or lacking at some part of the circumference (fig. 11). 
The explanation of this appearance must be that after the 
epidermis has extended over the pore canal the mesenchyme 
of the dermal membrane also extends in towards the middle of the 
canal, thus tending to obliterate it. 
Fortunately in this sponge the behavior of the pores may easily 
he watched during life. For this purpose an oscular tube is 
cut off , split lengthwise, and the halves mounted with epidermal 
surface uppermost in plenty of sea water under a coverglass. 
The cover flattens the pieces sufficiently to permit the use of a 
one-sixth inch objective. In such preparations made from 
a sponge just removed from the live box, many of the pores will 
be found open and their closure may be actually observed. I 
append the following records of observations on the closure of 
selected pores. 
Pore 1. At 9.45 a.m. the pore is open with one nucleus at the 
margin (fig. 10). The nucleus shifts its position traveling back 
and forth along the margin, going sometimes half round the pore 
and back again. The movements of the nucleus are quick and 
easily observed. At 9.50 the epidermis extends a short distance 
