538 
H. V. WILSON 
close to the surface, and as is customary in such sponges imper- 
fectly separate a thin superficial layer known as the dermal mem- 
brane from the inner mass of the sponge body. The dermal 
membrane contains no flagellated chambers, or only a very few 
scattered here and there, and is made up of a thin sheet of mesen- 
chyme containing spicules, which is covered on the outer surface 
by the epidermis and on the inner surface by the epithelioid mem- 
brane forming the wall of the subdermal space (and of the canals 
in general). According to the current conceptions of the histo- 
logical structure of sponges we would expect to find the epidermis 
and canal walls both to consist of a single layer of flat epithelium 
cells (pinacocytes). 
Actually I find that the epidermis of this sponge consists of 
a thin protoplasmic sheet studded with nuclei and exhibiting 
absolutely no cell boundaries. It is a syncytium. Cell bound- 
aries are sometimes overlooked but it seems to me that the variety 
of histological niethods I have practiced makes it certain that 
cells do not exist. 
Results with material fixed in alcohol 
Comparison with living tissues shows that strong alcohol, ab- 
solute or 95 per cent, is an excellent fixative for sponge tissues. I 
use it in liberal quantities, and very shortly after the immersion 
of the piece of sponge, change to fresh alcohol, changing again 
after a few hours. The precipitate which alcohol unfortunately 
causes in sea water has scarcely time to settle on the sponge if 
the first change be made quickly. Moving the piece about in the 
alcohol also helps to keep the surfaces clear of the precipitate. 
Suitable pieces were stained in toto with haemalum and were then 
imbedded, some in celloidin, some in paraffine. On the whole I 
recommend the celloidin, but the paraffine preparations were 
satisfactory. After the xylol bath I add soft (40° melting point) 
-paraffine to the xylol, warm the mixture up gradually, and imbed 
30 minutes in soft and 30 minutes in harder (50°-55° melting 
point) paraffine. Very thick tangential sections are made. Such 
