L. Harrison 
113 
ill Gyropus ovalis, showing a chitinous tab resting upon an extremely 
narrow tracheal neck, and having attached to it distally a muscle, the 
other insertion of which is not indicated beyond a vague statement 
that it runs to the integument. Similar figures are given for various 
Anoplura. Mjoberg points out {l.c. p. 222) that his observations are 
confined to the Amblycera, the opaque integument hindering them 
in the Ischnocera. I was for some time at a loss to reconcile Mjoberg’s 
statement and figure with my own observations in sections of Ischno- 
ceran forms, or to understand exactly how occlusion was brought about. 
His figure affords no apparent fulcrum for the leverage exerted by the 
Fig. 15. Occluding apparatus of Gyropus ovalis, after Mjoberg. 
Fig. 16. Stigma and occluding apparatus of Trichodectes lotiyicornis, .semi-diagrammatic ; 
(A) open; (B) closed. 
tab. After some difficulties, due to the small size of the structures 
involved, and the very serious hindrance to the cutting of good sections 
which the thickness of the chitinous cuticle presents, 1 have succeeded 
in demonstrating at least two types of occluding apparatus, a simple 
and a more complex; with possibly some intermediate forms, but on 
these my observations are not complete. 
The simple type is that figured by Mjoberg for Gyropus ovalis. 
I give his version in Fig. 15. Fig. 16 gives a diagrammatic view of 
the stigmatic apparatus open and closed in a species of Trichodectes. 
It vfill be seen that a long narrow rigidly chitinous bulla follows the 
Parasitology vm 
8 
