422 Dr. David Sharp on tJie structure of the 



number of Coleoptera are provided with special cavities, 

 in which they can withdraw the sensitive portions of the 

 antenna ; and in many cases complete protection is 

 obtained for the sensitive parts of the mouth by various 

 modifications for retracting the mouth within the thoracic 

 cavity, or under protection of a projecting part of the 

 thorax (the chin-piece in Histeridce and Elateridce, for 

 example), or by inflecting the head in a peculiar man- 

 ner. The modifications of some parts of the skeleton for 

 these purposes is truly marvellous, as any one who has 

 examined the extraordinary modifications of the sternum 

 in the Anohiidce will admit ; and it is therefore quite 

 consistent with what we find to obtain in insect economy 

 that the alimentary canal at the other extremity of the 

 body should be made to protect the oedeagus, and the 

 fact justifies us to some extent in inferring that the 

 oedeagus, or some part of it, is a sensitive organ ; but it 

 is, on the other hand, equally probable that the delicate 

 structures of the oedeagus are covered simply to preserve 

 them from injury. 



I have stated, in speaking of the rectal-cauda, that 

 in many forms it does not extend to the extremity of 

 the body, but terminates in the middle of the genital 

 segment. This certainly is a very curious arrangement, 

 and at present I am not able to state any incontrovertible 

 reason for the abbreviation. Evidently the cauda, — i. e, 

 the alimentary canal, — ought to extend to the extremity 

 of the body ; for it does so in the female Pentatomidce in 

 a conspicuous manner, and it does so in the males of 

 many species. It would hence appear that its abbrevia- 

 tion in some forms must be looked on as a departure 

 from the natural arrangement of the parts. And it 

 must be considered a very peculiar departure, for it is 

 difficult to understand how in such cases the excre- 

 mentitious matter is extruded entirely from the body. 

 Mr. Champion tells me that he is under the impression 

 that some bugs have the power of forcibly ejecting the 

 excrementitious matter by a sort of squirting process ; 

 but if this be the method employed in the Scutellerina, 

 it must be accompanied by a process of simultaneously 

 spreading the wings so as to get their tips out of the 

 way, while at the same time the genital segment must 

 be greatly exserted so as to extend it beyond the 

 tip of the scutellar covering of the body. I have 



