HERPYLLOBIUS ARCTICUS. 
393 
witli muscles. The external skin is continuous down the 
stalky at the end of which it becomes chitinous, and, turning 
up, forms a collar (Kroyer’s “sucker ”), which is embedded in 
the tissue of the host, and acts as a hold-fast. Some of 
the internal organs run down the stalk and are directly 
continuous with those of the root system. 
When cut in sections and examined under the microscope, 
the cuticle of these animals appears as a thick layer, slightly 
chitinous and traversed by a number of fine wavy fibres 
running parallel to the surface ; externally it is bounded by a 
thin layer which stains more deeply than the rest of the 
skin. 
Lying beneath the cuticle and at intervals sending up fine 
processes into it is a thin layer (PI. 22, fig. 6, hyp.) with 
nuclei scattered along it; it usually appears to be without any 
definite structure except in one case (PI. 22, fig. 4, hyp.), when 
in longitudinal section this layer appears to be composed of 
epithelial cells; longitudinal sections of other individuals, 
however, do not show this structure. This layer probably 
represents tlie hypodermis, but it shows a tendency to shrink 
away from the cuticle and applies itself closely to the internal 
organs; the pi-ocesses running into the cuticle may be caused 
by a folding of the sections. In the anterior region of this 
external portion some sections show canal-like openings 
through the skin, but there is no alteration in the tissues 
below them, so it is likely that these are also due to folding 
caused by shrinkage. 
Posteriorly there are several chitin-lined apertures (Text- 
fig. 1), according to Jensen (6) six in number, to which, he 
says, are attached the males, although they are not the 
genital openings. Opening into each of these there is a peculiar 
gland, which he figures (6, Tab. ii, fig. 12). I have examined 
these glands in my own sections and can find no other opening 
except tlirough these apertures. 
The genital openings are large slits placed on the end of 
the chitinous supports of the egg-sacs, and from them a duct 
may be seen running to the inside of the animal where it 
