560 
H. V. WILSON 
The final result, complete closure and obliteration of the pore 
canal, which may occur as the end of a series of easily distinguished 
steps, is in other cases brought about simply through continued 
shrinking (pore 2, for Lissodendorj^x) . Or the pore canal may 
shrink greatly, and then be closed in by the formation of a pore 
membrane (fig. 18, for Lissodendoryx), the complete obliteration 
occurring later. 
TPIE CANAL EPITHELIUM IN STYLOTELLA 
Oscular lobes of sponges in which the canals were well expanded, 
were fixed in alcohol (absolute and 95 per cent), sublimate, and 
picro-sulphuric. After hardening pieces were excised which in- 
cluded two or three of the main efferent canals, and these were 
sectioned so as to cut the canals longitudinally. Celloidin was 
used as an imbedding material, and the sections were cut thick. 
As the series of sections passes through a canal, the first and last 
sections will of course cut the canal wall tangentially, and these 
sections when mounted with the canalar face up give excellent 
surface views of the lining. For staining haemalum was used 
^'in toto," and the sections were stained in congo red. It is only 
the main efferent canals that I have studied. 
Pieces fixed in alcohol and picro-sulphuric yield essentially the 
same results. A study of the details shows further that the results 
are reliable. The main efferent canals are lined with the epithe- 
lial membrane depicted in fig. 20. It may be seen that the mem- 
brane consists of a single layer of flattened cells that are separated 
by wide spaces across which abundant intercellular connectives 
pass. The cells are in general elongated in a direction transverse 
to the long axis of the canal, but polygonal cells also occur. The 
cytoplasm is granular and vacuolated, and quite without distinct 
boundaries. It passes insensibly into the intercellular connectives. 
-The vacuoles vary in size and are irregularly distributed. In many 
cells the granules are scattered more or less uniformly through the 
cell, but quite commonly they are distributed in dense and pretty 
straight tracts which often extend along one margin. The nuclei 
appear to be all alike. They uniformly show the membrane. 
