L. E. Robinson and J. Davidson 
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of the parts of Gent’s organ with the general integument of the body, 
and is complicated by the continuity of the two sacs with the hypo- 
dermis and cuticle of the body wall. In this section, the glandular 
portion ( gl. Gen. org.) is cut in a plane slightly anterior to its connection 
with the hypodermal sac, and appears, therefore, to be completely 
separated from the latter. 
From a study of these sections, the thin walls of the chitinous sacs 
are seen to be folded in a very curious manner, and it may be observed 
that many of these folds are absolutely constant in their forms and 
relations, in different individuals. In the mesial portion, where, it will 
be noticed, the chitinous membrane is stouter than elsewhere ( ct. s'.), 
a number of longitudinal folds appear (see also Plate XXVI, fig. 8), 
which in transverse section present an S-shaped figure. These folds 
extend from the mouth of the chitinous sac almost to its posterior 
extremity, and, unlike the thin and flexible membranous chitin which 
forms the major part of the sac, they are sufficiently stiff and substantial 
to maintain their form, or at least are able to resume their original 
form, by virtue of their elasticity, when the everted sac returns to the 
resting state. A small portion which is thrown into a series of fine 
longitudinal folds may always be observed lying close to the S-shaped 
folds; these are shown in the lower section (Plate XXVIII) as a series 
of small regular undulations. What the functions of the stiff folds of 
the chitinous sac may be, we cannot determine with certainty, but it 
is suggested that they are concerned in some way with the restoration 
of the everted chitinous sac to its resting position. A small salient 
longitudinal fold of the wall of the hypodermal sac extends into the 
space formed by the curve of the lower limb of the S-shaped fold, and, 
in all probability, assists in maintaining the chitinous sac in a correct 
position during the resting state. This hypodermal fold appears in the 
sections as a small tongue-like extension from the inner surface of the 
hypodermal sac (see Plate XXVI, fig. 9 ; and Plate XXVIII). 
The glandular portion of Gene’s organ (gl. Gen. org.), as already 
has been shown, opens into the space between the hypodermal and the 
chitinous sacs. The gland proper is divided in a digitate manner into 
a number of simple tubules with thick walls and blind extremities. 
These tubules extend laterally and posteriorly within the body cavity, 
and in the active phase of the organ may attain a very considerable 
size. Each tubule is lined with a thick secretory epithelium composed 
of large columnar cells (see Plate XXVI, fig. 10), the bases of which 
rest on a thin homogeneous basal membrane which forms the covering 
