.ON ONCHNESOMA STEENSTRUPII. 235 
the body. The skin of the introvert, when extended, is trans- 
parent, so that the esophagus and nervous system may be seen 
through it. 
There is a marked thickening of the skin where the introvert 
joins the body; the anus is situated a little anterior to this. 
The external opening of the kidney is a little behind, just to 
the side of the ventral nerve-cord. 
Tue STRUCTURE OF THE SKIN. 
The layers which compose the skin of Onchnesoma have 
been described by the Norwegian writers ; there are, however, 
one or two details which may be added to their account. As 
in the skin of other Sipunculids, we meet with six layers. 
The state of preservation of my specimens did not allow the 
epidermal cells to be made out. But this outermost layer of 
cells probably forms part of the deeply stained external layer 
seen in fig. 6. 
In section this layer appears ridged, the ridges corresponding 
with the wrinkles on the surface of the animal. It is obscured 
by a number of granules, which stain very deeply with hema- 
toxylin; these granules are apparently produced by certain 
structures which correspond with the epidermal glands of 
other forms. Between the darkly stained external layer 
and the circular muscles is a thick gelatinous connective- 
tissue layer, or cutis, in which hardly any trace of cells 
could be detected. At the base of this the skin glands are 
situated. 
The state of the preservation of my material did not allow 
me to see this point very clearly, but I have no doubt that the 
epidermal glands are composed of specialised epidermal cells. 
Each gland is ofa spherical shape; from the outer edge of this a 
duct with sharply defined outline leads through the cutis to 
the surface of the body. Within the glands lie numerous darkly 
stained granules, similar to those which cover the outside of 
the body ; and there is little doubt that the latter have their 
origin in these structures, and pass out with the mucus which 
