550 
H. V. WILSON 
THE EPIDERMIS IN RENIERA 
The species used is an undescribed one fairly common in Beau- 
fort harbor. The body, frequently about 100 mm. high, is a 
complex system of anastomosing cylindrical branches, the diame- 
ter of which varies from about 3 mm. to 8 mm. The color is 
often pink but varies to a brown. The oscula terminate short 
tubes arising vertically from the branches. Such oscular tubes 
are frequently 1.5-3 mm. in diameter, 2-4 mm. high. The wall 
of the tube is colorless, thin, and transparent. The sponge, like 
the other two forms used for the observations recorded in this 
paper, falls in the halichondrine monaxonida. 
For the study of the epidermis pieces were fixed in absolute 
alcohol, 95 per cent alcohol, sublimate, picro-sulphuric. Thick 
tangential sections were made from the smoothest and most 
transparent parts of the surface. Both celloidin and paraffine 
were employed. Useful preparations were also made du'ectly 
from the oscular tubes in the following way. The tube was cut 
off, split lengthwise, the sponge tissue picked away from the ca- 
nalar surface, and the pieces mounted with the epidermal surface 
uppermost. For staining I made use in general of haemalum 
and Congo red, staining the piece in toto with haemalum and the 
sections in congo. 
Results with material fixed in alcohol 
Alcohol proved much the best fixative. The epidermis is so 
delicate a membrane that during the treatment necessary with 
other fixatives it cracks. In the alcoholic preparations clean 
places must be looked for. These are abundant enough, and in 
such places the structure of the layer may be successfully studied. 
There are no cell boundaries. The layer is a syncytium as in 
Stylotella, consisting of a thin, continuous sheet of protoplasm 
containing abundant nuclei that are irregularis^ scattered (fig. 
11). Round each nucleus as a rule the protoplasmic sheet is 
thicker than elsewhere, takes a deeper stain, and presents a finely 
granular appearance. The rest of the sheet is minuteh' reticular. 
