546 
H. Y. AVILSON 
REGENERATION OF THE EPIDERMIS IN STYLOTELLA 
A dermal membrane with normal epidermis soon regenerates 
over a cut surface. For the stud}^ of the process of regeneration, 
sections vertical to the surface are of little use. Themethod 
I have followed was to allow the regeneration to proceed a certain 
tinie, then to fix and harden the piece of sponge, and to cut from 
the superficial region a number of thick (100m) tangential sec- 
tions. For the fixation alcohol, picro-sulphuric and sublimate 
were employed. The piece was stained in toto with haemalum, 
and the sections with congo red. Paraffine and celloidin sec- 
tions were chiefly used, but good preparations were sometimes 
made by slicing off free-hand the regenerating surface from the 
piece in alcohol, and at once staining and mounting the slices. 
Or the piece was fixed in glacial acetic, washed in water, and the 
regenerating surface sliced off. The sponge parenchyma was 
then picked away with needles and forceps from the surface layer, 
which was later stained and mounted in glycerine. 
The original cut surface was made as smooth as possible, and 
all of it is included in the first few sections. These are mounted 
with the regenerating surface uppermost. Where the surface 
was part of the choanosome such preparations are too opaque for 
study. But where the surface was part of the transparent col- 
lenchyma, the sections offer fairl}^ clear pictures. Much the 
best pictures of all are to be had from the new derm^al membrane 
which develops across the cut ends of the larger canals. To ob- 
tain membrane of this kind I cut off oscular lobes about an inch 
below the apex, thus cutting the main efferent canals transversely. 
The open ends of the canals become closed in by the new mem- 
brane which extends out from the surrounding collenchyma 
across the aperture. The rate at which the canals become closed 
in may be gathered from the following record. The lobes were 
cut off at 9 . 30 a.m., the cut surface of each lobe showing several 
widely open canals. At 1.30 p.m., most of the canals were closed 
in by thin, collenchymatous membranes perforated in the centre 
like diaphragms. In the case of a few canals the membranes had 
completely closed the apertures. Within an hour or two all of 
