480 Mr. D. Sharp and Mr. F. Muir on the Comparative 
speculative opinions on the same subject are given; but 
a brief elementary statement on this point will probably 
be found useful here. Two simple diagrams (figs. 239 
and 239) have been made with the same object. They are 
really diagrammatic and do not represent any particular 
form. 
Let a glove be taken, a hole pierced in the tip of one 
of its fingers, a slender tube attached around this hole, 
this tube being placed inside the finger and prolonged 
into the hand-part of the glove: and we have before us 
a rough model of the genital tube. 
This structure lends itself to modification in the readiest 
manner. By traction on the slender tube the finger of 
the glove can be entirely drawn into the hand, with the 
result that the distal orifice becomes proximal. Let the 
glove finger be restored to its natural position and some 
hard patches be put on it, and the operation of invagina- 
tion be again repeated, and it will be noted how protean 
this simple arrangement can become. Further make some 
small folds on the finger, andisuppose these to grow out 
(after the fashion of the horns and processes on the heads 
of Lamellicorn beetles) and the reader will then have a 
general idea of the structures we are about to consider. 
The finger of the glove can be made by some folds to 
collapse in several layers, like a shut-up nautical telescope, 
and this telescopic arrangement can be carried to such an 
extent that Straus-Durckheim (M/elolontha vulgaris, pl. vi, 
f. 1) shows in a section of the telescopically collapsed tube 
no less than eleven superposed layers. 
We scarcely need to remark that the retraction and 
eversion of the genital tube are not brought about by 
force applied to the duct. 
We have had considerable difficulty in arranging our 
matter in a comprehensible sequence, and the different 
sections of the memoir are not conformable in this respect. 
We have endeavoured to diminish the inconvenience 
resulting from this by means of an alphabetical index 
of the names of families and groups placed immediately 
before the explanation of the figures. 
In the course of this memoir we have occasion to refer 
the reader to a passage of the historian Gibbon, relating 
to the Empress Theodora, the consort of the Emperor 
who rebuilt the great cathedral of Saint Sophia at 
Constantinople. We may fittingly close our introductory 
