424 Dr. David Sharp on the structure of the 



and are always fixtures, may be of the nature of supports 

 or holdfasts. My suggestion as to the protective func- 

 tions of some of the parts is, I think, of importance ; 

 this, indeed, is probably one of the reasons why the 

 structures I have been speaking of differ so much in 

 their general arrangement from what they do in the 

 other orders of insects. In the Coleoptera, for instance, 

 protection is obtained by withdrawing the whole of the 

 male organs and their accessory parts into the interior 

 of the body ; whereas in the Hemiptera the organs are 

 not withdrawn into the body to an extent sufficient to 

 protect them ; and it appears probable that the cavity 

 in which they are lodged is a special outgrowth for their 

 protection and accommodation. According to embryo- 

 logical data obtained in other insects the oedeagus was 

 originally , wholly or in part, an external organ of the nature 

 of an appendage, and if this be the case, the mode of 

 evolution of forms in which it is now drawn completely 

 — with all its complex accessory parts — into the interior 

 of the body must have been totally different from the 

 development in the Hemiptera, where it remains homo- 

 logically an external organ, with special arrangements for 

 covering it. 



The aesthetic aspect of the arrangement in many of 

 the higher species, such as Catacanthiis, Nezara, and 

 Edessa, is very remarkable, but I do not think there is 

 at present evidence that would justify us in attaching 

 any special biological importance to it. It certainly is 

 a most remarkable fact that the posterior part of the 

 alimentary canal should be used as an external organ 

 for the protection of other parts, and that it should 

 become adorned with bosses and projections symmetri- 

 cally formed and elegantly ciliated ; and the idea is 

 almost suggested that these peculiarities are of use in 

 producing some impression on the other sex. But I 

 think this idea may be dismissed as in all probability 

 quite untenable. 



Not the least curious point in these organs is the great 

 variety of forms they present. The variations in the 

 shapes of the lateral appendages and of the inferior 

 process are truly extraordinary, but they are insignificant 

 as compared with the extreme differences that exist in 

 the oedeagus itself. If this organ, as seen in EustJiencs 

 pratti, in Stilida indccora, Edessa ruJ'o-mar(jinata, Pcecilo- 



