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 239ft) 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 band, 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, and [suppose 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 (Melolonfha vulgaris, pi. 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 endeavoui'ed 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 



